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	$244.41	4.389%	$255.1372	$255.14	$255.15	$255.10
Purchase #2	$247.59	4.140%	$257.8402	$257.84	$257.85	$257.80
Purchase #3	$199.85	5.874%	$211.5892	$211.59	$211.60	$211.60
Purchase #4	$214.28	4.294%	$223.4812	$223.48	$223.50	$223.50
Purchase #5	$159.66	8.753%	$173.635	$173.64	$173.65	$173.60
Purchase #6	$83.30	4.827%	$87.3209	$87.32	$87.30	$87.30
Purchase #7	$57.62	13.621%	$65.4684	$65.47	$65.45	$65.50
7 purchase totals =	$1,206.71		$1,274.4721	$1,274.48	$1,274.50	$1,274.40