Lying is a sin, but

Lying is a sin according to the law.

Leviticus 19:11 Ye shall not steal, neither deal falsely, neither lie one to another.

But it is, as all other sins, forgiven in the New Testament.

If in the flesh you have to lie, go by the new commandments, love God, and love your neighbor.

Matthew 22:40 On these two commandments hang all the law and the prophets.

Proverbs 10:12 Hatred stirreth up strifes: but love covereth all sins.

Some lies are even beneficial, for example:

Tamar lied, because of her love for God (Genesis 38).

Rahab lied, because of her love for her neighbor the two spies (Joshua 2).

They are both included in the book of the generation of Jesus Christ (Matthew 1).