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	$122.62	6.161%	$130.1746	$130.17	$130.15	$130.20
Purchase #2	$197.95	12.411%	$222.5176	$222.52	$222.50	$222.50
Purchase #3	$144.78	4.556%	$151.3762	$151.38	$151.40	$151.40
Purchase #4	$76.85	10.317%	$84.7786	$84.78	$84.80	$84.80
Purchase #5	$223.72	4.519%	$233.8299	$233.83	$233.85	$233.80
Purchase #6	$111.49	12.481%	$125.4051	$125.41	$125.40	$125.40
Purchase #7	$39.41	10.637%	$43.602	$43.60	$43.60	$43.60
7 purchase totals =	$916.82		$991.6840	$991.69	$991.70	$991.70