A tithe is 10 percent of your increase (this is before your deductions, insurance, etc). 

 The Church upholds the biblical teaching that tithing is a command instituted by God for doing His work and caring for His Church.

• Deuteronomy 14:22 teaches, “You shall truly tithe all the increase of your grain that the field produces year by year” (emphasis added). Based on this clear and direct biblical guideline, we see that we should calculate our tithe based on our “increase.” Increase is determined by any profit or earning we receive after we have subtracted the cost of doing business or the cost of investing in any work or investment activity.

• If you receive a free gift, you do not pay tithe on it. That includes an inheritance. It is not necessary to give a tithe on a gift or any form of gratuity for which you do not perform some type of service. However, it would be appropriate to show thanks to God by giving an offering for having been blessed with a substantial gift.

• Regarding the subject of income tax returns and stimulus. Technically, if you are paying tithing based on your gross income and you get a tax return  then you wouldn't need to pay any tithing on the tax return or the stimulus since you are already paying tithing as you receive your income this year. 

• Thus, even including that specific instance with the Levites, all tithing had to do with what an individual labored for—the increase from gleaning grapes (and producing wine), olives, barley, wheat and the like, to harvesting fruit from orchards, to the increase from year to year from cattle, sheep, goats, etc. We find no specific command given to the children of Israel, or to the Church, to pay tithes on an inheritance or any other gifts.

Again, however, an offering for an inheritance or other substantial gift could and perhaps should be considered. But such an offering and the amount given is totally up to the recipient of the gift.