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	$234.49	10.246%	$258.5158	$258.52	$258.50	$258.50
Purchase #2	$229.27	11.735%	$256.1748	$256.17	$256.15	$256.20
Purchase #3	$136.69	11.115%	$151.8831	$151.88	$151.90	$151.90
Purchase #4	$242.74	5.505%	$256.1028	$256.10	$256.10	$256.10
Purchase #5	$241.89	5.312%	$254.7392	$254.74	$254.75	$254.70
Purchase #6	$53.40	13.217%	$60.4579	$60.46	$60.45	$60.50
Purchase #7	$216.85	10.132%	$238.8212	$238.82	$238.80	$238.80
7 purchase totals =	$1,355.33		$1,476.6948	$1,476.69	$1,476.65	$1,476.70