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	$155.50	9.714%	$170.6053	$170.61	$170.60	$170.60
Purchase #2	$234.70	8.570%	$254.8138	$254.81	$254.80	$254.80
Purchase #3	$132.49	12.150%	$148.5875	$148.59	$148.60	$148.60
Purchase #4	$63.29	11.309%	$70.4475	$70.45	$70.45	$70.40
Purchase #5	$163.41	7.792%	$176.1429	$176.14	$176.15	$176.10
Purchase #6	$95.42	4.371%	$99.5908	$99.59	$99.60	$99.60
Purchase #7	$223.34	3.176%	$230.4333	$230.43	$230.45	$230.40
7 purchase totals =	$1,068.15		$1,150.6211	$1,150.62	$1,150.65	$1,150.50