Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.89	4.760%	$78.4548	$78.45	$78.45	$78.50
Purchase #2	$40.49	13.380%	$45.9076	$45.91	$45.90	$45.90
Purchase #3	$128.43	3.202%	$132.5423	$132.54	$132.55	$132.50
Purchase #4	$144.71	13.541%	$164.3052	$164.31	$164.30	$164.30
Purchase #5	$171.35	13.339%	$194.2064	$194.21	$194.20	$194.20
Purchase #6	$249.58	8.465%	$270.7069	$270.71	$270.70	$270.70
Purchase #7	$122.53	9.642%	$134.3443	$134.34	$134.35	$134.30
7 purchase totals =	$931.98		$1,020.4675	$1,020.47	$1,020.45	$1,020.40