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	$144.87	4.808%	$151.8353	$151.84	$151.85	$151.80
Purchase #2	$83.45	13.654%	$94.8443	$94.84	$94.85	$94.80
Purchase #3	$58.54	12.648%	$65.9441	$65.94	$65.95	$65.90
Purchase #4	$101.75	9.552%	$111.4692	$111.47	$111.45	$111.50
Purchase #5	$87.82	3.240%	$90.6654	$90.67	$90.65	$90.70
Purchase #6	$242.50	13.414%	$275.029	$275.03	$275.05	$275.00
Purchase #7	$129.28	7.255%	$138.6593	$138.66	$138.65	$138.70
7 purchase totals =	$848.21		$928.4466	$928.45	$928.45	$928.40