The biblical tithe is not merely ten percent of oneís increase; it is the first ten percent (Nehemiah 10:35-37). It is not an ordinance of New Testament law; it is an element of grace and truth, and should be done as an act of faith (John 1:16; Romans 4:12-14).
There is obviously much confusion about the doctrine of tithes, and many have been hurt by church leaders who club believers for not tithing or impose it on Godís people like a law. For a more detailed answer to your question, please read our article titled The New Testament Tithe. It can be found on Shelf 4 of the Apostolic Free Library.