Tithes were required in the Old Testament. 10% of animals and crops went to support the Levites.

(Leviticus 27:30-33 NIV) "'A tithe of everything from the land, whether grain from the soil or fruit from the trees, belongs to the LORD; it is holy to the LORD. {31} If a man redeems any of his tithe, he must add a fifth of the value to it. {32} The entire tithe of the herd and flock--every tenth animal that passes under the shepherd's rod--will be holy to the LORD. {33} He must not pick out the good from the bad or make any substitution. If he does make a substitution, both the animal and its substitute become holy and cannot be redeemed.'"

The word "tithe" doesn't even appear in the New Testament. You're free to give less or more depending on your circumstances.

(2 Corinthians 9:6-7 NIV) Remember this: Whoever sows sparingly will also reap sparingly, and whoever sows generously will also reap generously. {7} Each man should give what he has decided in his heart to give, not reluctantly or under compulsion, for God loves a cheerful giver.