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	$235.43	8.378%	$255.1543	$255.15	$255.15	$255.20
Purchase #2	$138.29	5.808%	$146.3219	$146.32	$146.30	$146.30
Purchase #3	$151.72	10.419%	$167.5277	$167.53	$167.55	$167.50
Purchase #4	$206.27	13.767%	$234.6672	$234.67	$234.65	$234.70
Purchase #5	$139.35	11.665%	$155.6052	$155.61	$155.60	$155.60
Purchase #6	$154.41	10.197%	$170.1552	$170.16	$170.15	$170.20
Purchase #7	$35.30	9.500%	$38.6535	$38.65	$38.65	$38.70
7 purchase totals =	$1,060.77		$1,168.0850	$1,168.09	$1,168.05	$1,168.20