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	$48.51	4.567%	$50.7255	$50.73	$50.75	$50.70
Purchase #2	$183.77	8.491%	$199.3739	$199.37	$199.35	$199.40
Purchase #3	$142.64	11.106%	$158.4816	$158.48	$158.50	$158.50
Purchase #4	$38.79	9.305%	$42.3994	$42.40	$42.40	$42.40
Purchase #5	$12.45	5.731%	$13.1635	$13.16	$13.15	$13.20
Purchase #6	$131.66	12.487%	$148.1004	$148.10	$148.10	$148.10
Purchase #7	$53.70	10.324%	$59.244	$59.24	$59.25	$59.20
7 purchase totals =	$611.52		$671.4883	$671.48	$671.50	$671.50