I suspect it depends on what you were fired for and if you think that would be a problem for your future employers. Chances are they will find out anyway if they contact them for a reference. If you feel you could offer a sensible explanation in mitigation then tell them.
If you are questioned directly 'Why did you leave your last job?' you have a choice - tell the truth or ignore the question.
Anything else would be a lie and the previous employers are likely to be contacted for references.
Best to tell the truth, but you can moderate your reply and expand if necessary. If you were fired for bad timekeeping for example, you can add a note that you had problems which are now resolved and will not re-occur.