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	$243.53	12.301%	$273.4866	$273.49	$273.50	$273.50
Purchase #2	$62.44	6.614%	$66.5698	$66.57	$66.55	$66.60
Purchase #3	$136.65	9.605%	$149.7752	$149.78	$149.80	$149.80
Purchase #4	$97.89	11.248%	$108.9007	$108.90	$108.90	$108.90
Purchase #5	$211.40	10.770%	$234.1678	$234.17	$234.15	$234.20
Purchase #6	$158.80	4.355%	$165.7157	$165.72	$165.70	$165.70
Purchase #7	$111.98	11.829%	$125.2261	$125.23	$125.25	$125.20
7 purchase totals =	$1,022.69		$1,123.8419	$1,123.86	$1,123.85	$1,123.90