Although the tithe is not mentioned (in the New Testament), the giving of weekly offerings is (1 Cor. 16:2). And more importantly, it is generally the case that in the New Testament the obligations of the Old Testament legislation are heightened rather than lessened. That is, the law is interpreted in the fullest measure. So while we are not required to give a specific tenth of our income, it is hard to think of a normal Christian, blessed with the fullness of the Gospel of Jesus Christ, doing less. Under reasonable circumstances any true believer in Christ should give more than the tenth, for all we have is the Lord's.