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	$248.85	10.568%	$275.1485	$275.15	$275.15	$275.10
Purchase #2	$108.46	13.454%	$123.0522	$123.05	$123.05	$123.10
Purchase #3	$248.39	4.325%	$259.1329	$259.13	$259.15	$259.10
Purchase #4	$154.64	7.655%	$166.4777	$166.48	$166.50	$166.50
Purchase #5	$89.39	11.573%	$99.7351	$99.74	$99.75	$99.70
Purchase #6	$83.47	5.347%	$87.9331	$87.93	$87.95	$87.90
Purchase #7	$249.74	9.749%	$274.0872	$274.09	$274.10	$274.10
7 purchase totals =	$1,182.94		$1,285.5667	$1,285.57	$1,285.65	$1,285.50