Worldly truth is not absolute truth. Absolute and Eternal Truth is only Vaheguru Himself as stated in the first Salok of Siri Jap jee Sahib:
ਆਦਿ ਸਚੁ ਜੁਗਾਦਿ ਸਚੁ ॥ ਹੈ ਭੀ ਸਚੁ ਨਾਨਕ ਹੋਸੀ ਭੀ ਸਚੁ ॥੧॥
Sach or Truth according to Gurbani is such thing that does not change over time. Anything that you see in the world changes with time, therefore, there is nothing Sach in this world. If you look outside your window, you may see trees and buildings but next day if you see outside your same window, you may still see the same tree but the composition of that tree may have changed. It may have dropped some leaves or even branches. This means that the scene that you saw yesterday is no longer there which means that the scene that you saw yesterday was Mithiya or false. Similarly, since, the scene that you are beholding now, will change tomorrow, therefore, what you are seeing is false. This is why Gurbani has declared that anything that is visible to these worldly eyes is not Truth and is Mithiya:
ਦ੍ਰਿਸਟਿਮਾਨ ਹੈ ਸਗਲ ਮਿਥੇਨਾ ॥
(All that is visible is Mithena i.e. false.)
Now let's talk about an event. If five people witness an event, a dispute or an occurrence, all 5 people will have a different understanding of it. The 6th witness i.e. Vaheguru alone has the true understanding of any event or occurrence. In a dispute, we see that the parties involved consider themselves totally correct but it is Vaheguru jee alone who knows the true Truth and that's how he does justice. Our views of point, with respect to a worldly event or a thing are incomplete and for this reason are not Truth.
What the eyes see may be false and what the ears hear may be wrong. The reason is that what we may be viewing or hearing could only be part of the whole thing. A person in anger may say to his loved one, "I hate you". The lips may be saying, "I hate you" but the heart may not agree because what a person says under the influence of one of the 5 Bikaars, is not true. When anger or Krodh subsides, then the person realizes what one has said and is then filled with remorse. A person who witnesses the angry person saying that "I hate you" to his wife, may think that this person only hates but the truth of the matter may be quite the opposite. Under the influence of Kaam, one may say that you are very beautiful but when the Mantra of Kaam subsides, then he may not find you attractive. It's all jhooth, koor, and Mithiya.
The above Vichaar proves that anything that we see through our false Gyaan Indray (5 Senses) is not complete truth, rather totally false. So the worldly truth or false means nothing.
A Gursikh is equipped with a filter called Gurmat Bibek. Everything a Gursikh does or thinks is through this filter. A Gursikh is not dishonest or honest in worldly sense. Gurmat Bibek is what dictates how a Gursikh acts or not acts. The intention of a Gursikh is to live life according to principles of Gurmat. Honesty, care, compassion, charity etc. are natural side effects of following Gurmat, which includes primarily Naam and Gurbani.
About 22 years ago, I had been blessed with Amrit recently but had not come into Jatha yet and did not know too much about Gurmat. One of my friend was a Pakistani guy back then. He had a court case and persuaded me to go to the court as a witness for him. Basically, he wanted me to lie for him, in the court. I did not think too much about it and agreed to be his witness. In the court, when I took stand, they asked me to swear by Bible to tell the truth. I informed them that I had no faith in Bible. At this the judge asked me in whom I had faith. I replied that I had faith in my Guru - Guru Nanak. At this the judge asked me to affirm by Guru Nanak and give me account.
All of sudden, I realized what predicament I had got myself into. On one hand was my friend and on the other hand it was my faith. If I had known that I would be made to say something in the name of my Guru, I would have never agreed to take this stand. In the end, I could not ignore my Zameer (conscience) and told them the truth. It did not occur to me that I could have kept quiet. Due to my witness account, my friend was found guilty and had to pay a fine of few hundred dollars. I still remember how upset he got at me. We came out together and he started swearing at me. I apologised to him but to no avail. He angrily asked me why I had deceived him. I meekly replied with a low voice that my Zameer had awakened and I could not lie in the name of my Guru. He said, "ਓਇ ਕਮੀਨਿਆ ਤੇਰਾ ਜ਼ਮੀਰ ਅਜ ਹੀ ਜਾਗਣਾ ਸੀ। ਤੇਰੇ ਜ਼ਮੀਰ ਨੇ ਮੇਰਾ ਕੂੰਡਾ ਕਰ ਦਿਤਾ ਹੈ।" (O Kaminay, your Zameer had to awaken today only? Your zameer has caused me big loss). He said many other things that I meekly kept listening. We stayed friends and later on we used to laugh a lot at this incident. He pledged that he was never going to trust me in cases of courts as my Zameer was too dangerous.
One thing that I learned from Bhai Jagtar Singh jee was that a Gursikh should not deceive anyone, even the government. He was very strict in paying all taxes due to the government. He was a farmer and all of his income was pretty much cash. Other farmers, hardly pay any taxes because there is no proof of their income but Bhai Sahib was so meticulous that he used to keep account of even one cent and paid full taxes, on all his income. In one year, he had a lot of loss and his income was very low but that did not prevent him from not paying his full taxes. While doing Sewa for Punj Pyare and during the Sudhaaee of Punj Pyare, it was ensured that Gursikhs who don't pay full taxes are not allowed to do Sewa in Punj. One Gursikh had a very profitable business but he was not paying full tax. During the Sudhaaee this issue came up and Bhai Sahib said that what happens if a Gursikh not paying taxes and doing fraud with the government gets caught? Would it not bring bad name to the whole community and give a chance to people to say that a Gursikh doing Sewa in Punj Pyare is doing fraud? This Gursikh too was a person who had Guru Sahib's Bhae-bhaavni (Fear and Love of Guru). This Gursikh eventually had to close down his business since it was no longer worth if he paid all taxes. Guru Sahib did Kirpa and this Gursikh had no financial difficulty.
There can be situations, where telling the truth can be considered stupidity and deceiving the Panth. Kharkoo Singhs, sometimes used to lie about the whereabouts of their companions and this seems perfectly fine. Telling the truth would bring much more negative Karma than telling a lie, in this case. But under the guise of this, a Gursikh should not make a habit of lying. Jhooth should be avoided as it is a big obstacle in spiritual progress.