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	$45.95	12.837%	$51.8486	$51.85	$51.85	$51.80
Purchase #2	$150.35	12.771%	$169.5512	$169.55	$169.55	$169.60
Purchase #3	$223.82	7.390%	$240.3603	$240.36	$240.35	$240.40
Purchase #4	$74.32	12.393%	$83.5305	$83.53	$83.55	$83.50
Purchase #5	$242.77	3.748%	$251.869	$251.87	$251.85	$251.90
Purchase #6	$52.82	12.730%	$59.544	$59.54	$59.55	$59.50
Purchase #7	$111.47	11.823%	$124.6491	$124.65	$124.65	$124.60
7 purchase totals =	$901.50		$981.3527	$981.35	$981.35	$981.30