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	$231.35	8.615%	$251.2808	$251.28	$251.30	$251.30
Purchase #2	$131.91	13.612%	$149.8656	$149.87	$149.85	$149.90
Purchase #3	$204.57	11.704%	$228.5129	$228.51	$228.50	$228.50
Purchase #4	$58.55	6.170%	$62.1625	$62.16	$62.15	$62.20
Purchase #5	$35.87	3.776%	$37.2245	$37.22	$37.20	$37.20
Purchase #6	$11.27	13.676%	$12.8113	$12.81	$12.80	$12.80
Purchase #7	$72.49	8.218%	$78.4472	$78.45	$78.45	$78.40
7 purchase totals =	$746.01		$820.3048	$820.30	$820.25	$820.30