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	$131.40	4.844%	$137.765	$137.77	$137.75	$137.80
Purchase #2	$155.42	10.795%	$172.1976	$172.20	$172.20	$172.20
Purchase #3	$51.26	7.852%	$55.2849	$55.28	$55.30	$55.30
Purchase #4	$105.40	5.607%	$111.3098	$111.31	$111.30	$111.30
Purchase #5	$125.45	10.437%	$138.5432	$138.54	$138.55	$138.50
Purchase #6	$37.85	7.671%	$40.7535	$40.75	$40.75	$40.80
Purchase #7	$235.27	9.116%	$256.7172	$256.72	$256.70	$256.70
7 purchase totals =	$842.05		$912.5712	$912.57	$912.55	$912.60