How much does an Apple TV 4K 64 GB cost with sales tax?

It depends entirely on where in the U.S it will be bought. What state and city?

Taxes in the U.S. vary by state and city. So without knowing where it will be bought there's no way to know the final price.

In which city or state will he go to an Apple Store? As various states have various tax rates.

Highest combined (city and state) sales tax is around 10%. so for a $199 purchase you're looking at around $210 final price.

That depends on the state. That depends on the (re)seller. That possibly depends on shipping. Note that Apple doesn’t ship internationally.

Sorry, not $220, not 210.