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	$246.69	4.139%	$256.9005	$256.90	$256.90	$256.90
Purchase #2	$206.90	10.500%	$228.6245	$228.62	$228.60	$228.60
Purchase #3	$112.72	9.369%	$123.2807	$123.28	$123.30	$123.30
Purchase #4	$106.77	13.230%	$120.8957	$120.90	$120.90	$120.90
Purchase #5	$123.70	3.748%	$128.3363	$128.34	$128.35	$128.30
Purchase #6	$195.85	9.723%	$214.8925	$214.89	$214.90	$214.90
Purchase #7	$158.91	11.822%	$177.6963	$177.70	$177.70	$177.70
7 purchase totals =	$1,151.54		$1,250.6265	$1,250.63	$1,250.65	$1,250.60