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	$50.52	10.472%	$55.8105	$55.81	$55.80	$55.80
Purchase #2	$218.54	6.801%	$233.4029	$233.40	$233.40	$233.40
Purchase #3	$132.46	10.373%	$146.2001	$146.20	$146.20	$146.20
Purchase #4	$91.50	8.619%	$99.3864	$99.39	$99.40	$99.40
Purchase #5	$124.35	4.662%	$130.1472	$130.15	$130.15	$130.10
Purchase #6	$172.39	5.257%	$181.4525	$181.45	$181.45	$181.50
Purchase #7	$30.94	12.376%	$34.7691	$34.77	$34.75	$34.80
7 purchase totals =	$820.70		$881.1687	$881.17	$881.15	$881.20