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	$64.93	12.276%	$72.9008	$72.90	$72.90	$72.90
Purchase #2	$108.76	10.388%	$120.058	$120.06	$120.05	$120.10
Purchase #3	$27.71	5.437%	$29.2166	$29.22	$29.20	$29.20
Purchase #4	$165.71	7.455%	$178.0637	$178.06	$178.05	$178.10
Purchase #5	$169.77	13.624%	$192.8995	$192.90	$192.90	$192.90
Purchase #6	$89.26	8.603%	$96.939	$96.94	$96.95	$96.90
Purchase #7	$105.45	6.105%	$111.8877	$111.89	$111.90	$111.90
7 purchase totals =	$731.59		$801.9653	$801.97	$801.95	$802.00