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	$101.89	9.829%	$111.9048	$111.90	$111.90	$111.90
Purchase #2	$55.48	11.231%	$61.711	$61.71	$61.70	$61.70
Purchase #3	$17.59	8.413%	$19.0698	$19.07	$19.05	$19.10
Purchase #4	$143.86	5.379%	$151.5982	$151.60	$151.60	$151.60
Purchase #5	$24.55	7.262%	$26.3328	$26.33	$26.35	$26.30
Purchase #6	$89.34	13.230%	$101.1597	$101.16	$101.15	$101.20
Purchase #7	$100.48	5.247%	$105.7522	$105.75	$105.75	$105.80
7 purchase totals =	$533.19		$577.5285	$577.52	$577.50	$577.60