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	$211.78	8.823%	$230.4653	$230.47	$230.45	$230.50
Purchase #2	$101.90	10.317%	$112.413	$112.41	$112.40	$112.40
Purchase #3	$136.33	7.364%	$146.3693	$146.37	$146.35	$146.40
Purchase #4	$10.85	12.717%	$12.2298	$12.23	$12.25	$12.20
Purchase #5	$31.51	7.634%	$33.9155	$33.92	$33.90	$33.90
Purchase #6	$82.56	6.251%	$87.7208	$87.72	$87.70	$87.70
Purchase #7	$56.57	6.811%	$60.423	$60.42	$60.40	$60.40
7 purchase totals =	$631.50		$683.5367	$683.54	$683.45	$683.50