Price "Plus Tax"

$8.99 plus tax means: $8.99 plus an additional amount for tax. You pay more than $8.99, how much more they will compute for you automatically when you check out. The merchant keeps $8.99 of what you pay, and the rest they send to the city, county, state, or other sales tax district involved.

Fortunately cash registers are computerized. But some of us old geezers may remember how it was when computers took up an entire room, and a measly retail store did not have one.

You may sometimes see $8.99 no tax (for example paying on the internet to a merchant in a different state). Then you pay only the $8.99. And it is then your responsibility to pay the appropriate tax to the tax districts where you live. Some states make this easy to do; others less so.