"Side note: If you drop the penny, for the love of $diety change your sales tax structure so that it's a multiple of 5. 5%, 10%, 15%, etc."
I don't think you thought that through. Unless you are going to require prices be rounded to the nearest dollar, you still need pennies or even fractional pennies to accurately pay the tax. 15% of 75 cents is 11.25 cents, for instance.
I think what you do is that the government publishes a table of official roundoff values, so 15% of 75 cents becomes a thing that you look up in a table.
The last state I lived in where I looked closely at the sales tax structure had a table like this for which penny to round up or down to. It eliminated all formulas and ambiguity.
I don't think you thought that through. Unless you are going to require prices be rounded to the nearest dollar, you still need pennies or even fractional pennies to accurately pay the tax. 15% of 75 cents is 11.25 cents, for instance.