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	$99.65	12.343%	$111.9498	$111.95	$111.95	$111.90
Purchase #2	$133.35	6.816%	$142.4391	$142.44	$142.45	$142.40
Purchase #3	$121.80	9.747%	$133.6718	$133.67	$133.65	$133.70
Purchase #4	$97.54	3.313%	$100.7715	$100.77	$100.75	$100.80
Purchase #5	$124.75	10.208%	$137.4845	$137.48	$137.50	$137.50
Purchase #6	$27.33	12.213%	$30.6678	$30.67	$30.65	$30.70
Purchase #7	$14.29	8.527%	$15.5085	$15.51	$15.50	$15.50
7 purchase totals =	$618.71		$672.4930	$672.49	$672.45	$672.50