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	$223.81	12.422%	$251.6117	$251.61	$251.60	$251.60
Purchase #2	$117.70	10.322%	$129.849	$129.85	$129.85	$129.80
Purchase #3	$38.41	11.182%	$42.705	$42.71	$42.70	$42.70
Purchase #4	$49.57	13.323%	$56.1742	$56.17	$56.15	$56.20
Purchase #5	$122.25	12.850%	$137.9591	$137.96	$137.95	$138.00
Purchase #6	$172.79	11.150%	$192.0561	$192.06	$192.05	$192.10
Purchase #7	$244.79	12.546%	$275.5014	$275.50	$275.50	$275.50
7 purchase totals =	$969.32		$1,085.8565	$1,085.86	$1,085.80	$1,085.90