“Every tithe of the land, whether of the seed of the land or of the fruit of the trees, is the Lord’s; it is holy to the Lord. 31 If a man wishes to redeem some of his tithe, he shall add a fifth to it. 32 And every tithe of herds and flocks, every tenth animal of all that pass under the herdsman’s staff, shall be holy to the Lord. 33 One shall not differentiate between good or bad, neither shall he make a substitute for it; and if he does substitute for it, then both it and the substitute shall be holy; it shall not be redeemed.” Leviticus 27:30-33 (ESV)
Notice here that the tithe does not come from the wallet or the salary. There is no mention of the tithing of money in this summary at the very end of the book of Leviticus. The tithe comes from the “land”. It was the “seed” or agricultural products from the land that was holy to God and that was tithed. From the herds and flocks, the “tenth” animal that passed under the rod was holy and dedicated to God.