I also wanted to add, that Abraham's choice of not accepting gifts or payment from the King of Sodom, is a lot like Naaman's healing. Naaman was a non-believer. After Naaman was healed he believed. Elisha would not take "gifts," from Naaman because it would take away from the glory going to God. "Freely you have received, freely give.")
The battle that Abraham won, the glory was to be given to God. That is why he wouldn't accept anything from the King of Sodom.
So where and whom tithes or gifts come from is an important factor, as well as when they are acceptable.