Tithing was never an income or estate tax. It was the increase of the land - flocks and fields. That's all it was. It was required of the descendents of Jacob who inherited the land because Jacob vowed a vow to GOD to give to him the tenth of the land that GOD had just promised to give to him. Jacob didn't tithe because he didn't inherit the land.
And, behold, the LORD stood above it, and said, I am the LORD God of Abraham thy father, and the God of Isaac: the land whereon thou liest, to thee will I give it, and to thy seed; Genesis 28:13
And Jacob vowed a vow, saying, If God will be with me, and will keep me in this way that I go, and will give me bread to eat, and raiment to put on, So that I come again to my father's house in peace; then shall the LORD be my God: And this stone, which I have set for a pillar, shall be God's house: and of all that thou shalt give me I will surely give the tenth unto thee. Genesis 28:20-22