Tithing (or giving one tenth of one's income) finds its roots in the laws of the Old Testament.  There, it was a requirement for all members of the nation of Israel.  But are Christians required to tithe today? 

On the first day of every week each one of you is to put aside and save, as he may prosper.

1 Corinthians 16:2a NASB

This verse teaches that each individual should regularly set aside an offering in proportion to their income (how they are prospering). 

2 Corinthians 9:6-7 teaches that each person should give what is decided in his heart to give.  These verses also teach us to give generously.  In the New Testament, Christians are not mandated to tithe.  However, our offering comes from the heart.  We are compelled to give; not out of guilt but out of gratitude and love.

But who am I, and who are my people, that we should be able to give as generously as this? Everything comes from you, and we have given you only what comes from your hand.

1 Chronicles 29:14 NASB