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	$166.70	3.597%	$172.6962	$172.70	$172.70	$172.70
Purchase #2	$177.66	12.519%	$199.9013	$199.90	$199.90	$199.90
Purchase #3	$55.47	11.148%	$61.6538	$61.65	$61.65	$61.70
Purchase #4	$93.76	12.552%	$105.5288	$105.53	$105.55	$105.50
Purchase #5	$139.57	11.185%	$155.1809	$155.18	$155.20	$155.20
Purchase #6	$221.89	4.735%	$232.3965	$232.40	$232.40	$232.40
Purchase #7	$230.69	9.709%	$253.0877	$253.09	$253.10	$253.10
7 purchase totals =	$1,085.74		$1,180.4452	$1,180.45	$1,180.50	$1,180.50