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	$35.69	11.793%	$39.8989	$39.90	$39.90	$39.90
Purchase #2	$153.26	13.462%	$173.8919	$173.89	$173.90	$173.90
Purchase #3	$65.83	10.208%	$72.5499	$72.55	$72.55	$72.50
Purchase #4	$143.89	5.283%	$151.4917	$151.49	$151.50	$151.50
Purchase #5	$223.76	5.127%	$235.2322	$235.23	$235.25	$235.20
Purchase #6	$217.92	13.634%	$247.6312	$247.63	$247.65	$247.60
Purchase #7	$122.47	8.186%	$132.4954	$132.50	$132.50	$132.50
7 purchase totals =	$962.82		$1,053.1912	$1,053.19	$1,053.25	$1,053.10