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	$169.85	7.579%	$182.7229	$182.72	$182.70	$182.70
Purchase #2	$100.43	11.369%	$111.8479	$111.85	$111.85	$111.80
Purchase #3	$44.35	10.533%	$49.0214	$49.02	$49.00	$49.00
Purchase #4	$151.75	9.258%	$165.799	$165.80	$165.80	$165.80
Purchase #5	$32.77	8.260%	$35.4768	$35.48	$35.50	$35.50
Purchase #6	$25.43	13.813%	$28.9426	$28.94	$28.95	$28.90
Purchase #7	$44.38	13.175%	$50.2271	$50.23	$50.25	$50.20
7 purchase totals =	$568.96		$624.0377	$624.04	$624.05	$623.90