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	$11.31	11.300%	$12.588	$12.59	$12.60	$12.60
Purchase #2	$106.86	10.841%	$118.4447	$118.44	$118.45	$118.40
Purchase #3	$146.45	3.730%	$151.9126	$151.91	$151.90	$151.90
Purchase #4	$151.76	13.572%	$172.3569	$172.36	$172.35	$172.40
Purchase #5	$10.34	10.643%	$11.4405	$11.44	$11.45	$11.40
Purchase #6	$47.33	6.381%	$50.3501	$50.35	$50.35	$50.40
Purchase #7	$102.70	8.191%	$111.1122	$111.11	$111.10	$111.10
7 purchase totals =	$576.75		$628.2050	$628.20	$628.20	$628.20