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	$243.80	12.457%	$274.1702	$274.17	$274.15	$274.20
Purchase #2	$89.92	10.110%	$99.0109	$99.01	$99.00	$99.00
Purchase #3	$66.81	7.552%	$71.8555	$71.86	$71.85	$71.90
Purchase #4	$103.75	6.669%	$110.6691	$110.67	$110.65	$110.70
Purchase #5	$200.41	11.606%	$223.6696	$223.67	$223.65	$223.70
Purchase #6	$82.89	10.733%	$91.7866	$91.79	$91.80	$91.80
Purchase #7	$74.34	11.568%	$82.9397	$82.94	$82.95	$82.90
7 purchase totals =	$861.92		$954.1016	$954.11	$954.05	$954.20