It’s actually not 10 dollars, as even though you can round 9.99 up to make 10, to make that mathematically true all the time, you would have to change 9.99 to 9.99 reoccurring, which is something entirely different.
i mean in stores, they want the item to cost 10 dollars, but they have to charge tax, so they make it 9.99 and charge 1 cent tax to make it 10 dollars.