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	$204.31	10.453%	$225.6665	$225.67	$225.65	$225.70
Purchase #2	$38.82	4.251%	$40.4702	$40.47	$40.45	$40.50
Purchase #3	$63.51	9.569%	$69.5873	$69.59	$69.60	$69.60
Purchase #4	$235.36	12.838%	$265.5755	$265.58	$265.60	$265.60
Purchase #5	$105.52	10.574%	$116.6777	$116.68	$116.70	$116.70
Purchase #6	$30.46	7.766%	$32.8255	$32.83	$32.85	$32.80
Purchase #7	$200.64	13.240%	$227.2047	$227.20	$227.20	$227.20
7 purchase totals =	$878.62		$978.0074	$978.02	$978.05	$978.10