Where in the New Testament does it talk about tithing at 10 percent?

Tithing at 10 percent or any other percent is not mentioned anywhere in the New Testament.

Another Answer:

Tithing or giving is still part of the Christian way, though there is no mention of a strict 10 percent. This could be because by the time of Christ, the 10 percent 'tithe' was well established and He continued to follow the 'Law of Moses' or because Christ was now the new and Eternal High Priest (see Hebrews 7) and the Law is now 'filled to the top' (see Matthew 23:23) with the spiritual aspects therein. Consider this Scripture:

2 Corinthians 9:7New King James Version (NKJV)

7 So let each one give as he purposes in his heart, not grudgingly or of necessity; for God loves a cheerful giver.