Depends on the circumstances and your motivation for lying or telling the truth.
If someone is stealing at work, you should report it, assuming you have proof. It's morally and legally wrong for someone to steal something that isn't theirs--no matter how small the amounts. Small amounts can add up to large amounts very quickly. In that case, several people will be harmed, so you should speak up about it, even if it turns into a huge hassle. If some register is short simply because of human error, that's one thing. If you suspect someone is stealing, you need to address it right away, but don't openly accuse anyone unless you have proof. You might, after all, be mistaken about who the true culprit really is. But clearly, if you don't report it, you are allowing the theft to continue and that is also just as wrong.
If you're talking about withholding your opinion to spare someone's feelings, there's certainly not anything wrong with that. If Grandma gets a new dress she clearly loves, and shows it off to you, do you say, "Oh, God, that's HIDEOUS!" and completely hurt her feelings, spoil her fun, and crush her self-esteem? No. You say, "Wow, Grandma, that's one heck of a dress."
So lying isn't always bad; it all depends on your motives and the bigger picture.