Many churches teach that Christians are obligated to give a minimum of 10% of our income to our church. Others teach that preachers of these churches are turning the 10% tithe under the old covenant for Israel into a monetary legalistic prescription for Christians under the new covenant. I even heard a Pastor make a challenge to his congregation to give 10% of their income for 90 days and if God does not bless them then he will give them their money back.
In 2 Corinthians 9:5-7 we read: Therefore I thought it necessary to exhort the brethren to go to you ahead of time, and prepare your generous gift beforehand, which you had previously promised, that it may be ready as a matter of generosity and not as a grudging obligation. But this I say: He who sows sparingly will also reap sparingly, and he who sows bountifully will also reap bountifully. So let each one give as he purposes in his heart, not grudgingly or of necessity; for God loves a cheerful giver.
I don't see a "specific percentage" given anywhere for Christians to give under the new covenant, but I certainly believe in giving and not just to our church. I also believe that everything we own belongs to God and we certainly can't out give God.