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	$199.28	12.180%	$223.5523	$223.55	$223.55	$223.60
Purchase #2	$245.85	4.399%	$256.6649	$256.66	$256.65	$256.70
Purchase #3	$123.78	10.820%	$137.173	$137.17	$137.15	$137.20
Purchase #4	$221.76	13.596%	$251.9105	$251.91	$251.90	$251.90
Purchase #5	$51.53	9.390%	$56.3687	$56.37	$56.35	$56.40
Purchase #6	$81.46	12.313%	$91.4902	$91.49	$91.50	$91.50
Purchase #7	$36.51	8.208%	$39.5067	$39.51	$39.50	$39.50
7 purchase totals =	$960.17		$1,056.6663	$1,056.66	$1,056.60	$1,056.80