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	$30.43	10.826%	$33.7244	$33.72	$33.70	$33.70
Purchase #2	$39.43	10.375%	$43.5209	$43.52	$43.50	$43.50
Purchase #3	$125.78	3.316%	$129.9509	$129.95	$129.95	$130.00
Purchase #4	$146.55	6.218%	$155.6625	$155.66	$155.65	$155.70
Purchase #5	$117.82	10.471%	$130.1569	$130.16	$130.15	$130.20
Purchase #6	$205.71	9.517%	$225.2874	$225.29	$225.30	$225.30
Purchase #7	$151.81	13.389%	$172.1358	$172.14	$172.15	$172.10
7 purchase totals =	$817.53		$890.4388	$890.44	$890.40	$890.50