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	$41.41	12.379%	$46.5361	$46.54	$46.55	$46.50
Purchase #2	$70.83	9.729%	$77.7211	$77.72	$77.70	$77.70
Purchase #3	$177.36	4.580%	$185.4831	$185.48	$185.50	$185.50
Purchase #4	$45.61	7.193%	$48.8907	$48.89	$48.90	$48.90
Purchase #5	$137.55	6.733%	$146.8112	$146.81	$146.80	$146.80
Purchase #6	$70.78	10.418%	$78.1539	$78.15	$78.15	$78.20
Purchase #7	$46.55	12.814%	$52.5149	$52.51	$52.50	$52.50
7 purchase totals =	$590.09		$636.1110	$636.10	$636.10	$636.10