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	$37.59	10.439%	$41.514	$41.51	$41.50	$41.50
Purchase #2	$89.76	12.233%	$100.7403	$100.74	$100.75	$100.70
Purchase #3	$250.58	10.871%	$277.8206	$277.82	$277.80	$277.80
Purchase #4	$20.89	3.244%	$21.5677	$21.57	$21.55	$21.60
Purchase #5	$151.57	4.284%	$158.0633	$158.06	$158.05	$158.10
Purchase #6	$23.57	12.811%	$26.5896	$26.59	$26.60	$26.60
Purchase #7	$36.34	10.696%	$40.2269	$40.23	$40.25	$40.20
7 purchase totals =	$610.30		$666.5224	$666.52	$666.50	$666.50