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	$135.83	9.226%	$148.3617	$148.36	$148.35	$148.40
Purchase #2	$50.54	7.425%	$54.2926	$54.29	$54.30	$54.30
Purchase #3	$140.34	7.634%	$151.0536	$151.05	$151.05	$151.10
Purchase #4	$40.45	8.313%	$43.8126	$43.81	$43.80	$43.80
Purchase #5	$65.38	10.344%	$72.1429	$72.14	$72.15	$72.10
Purchase #6	$97.67	10.741%	$108.1607	$108.16	$108.15	$108.20
Purchase #7	$244.69	10.539%	$270.4779	$270.48	$270.50	$270.50
7 purchase totals =	$774.90		$848.3020	$848.29	$848.30	$848.40