First off we are not under a law of tithing. Second If one bother to read about the tithe, it was never money. There was no provision to give money. It was always product of farming, sheep, grain, wine so fourth. Even carpenters gave of their garden/farms. Also it was only heads of house holds, not servants or slaves or hired help.
We have something better now. We are able to give money, everyone who earns a wage can give and we can give according to our prosperity. And God does provide our needs when and makes a way as we give. But there is no promise to make one rich in worldly goods or money. The word say be content with food and clothes, Paul said he knows how to go without and to abound. All prosperity teachers are liars and false and pierce many through with thier false teaching.