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	$129.97	12.567%	$146.3033	$146.30	$146.30	$146.30
Purchase #2	$192.67	11.673%	$215.1604	$215.16	$215.15	$215.20
Purchase #3	$208.91	7.130%	$223.8053	$223.81	$223.80	$223.80
Purchase #4	$116.55	10.254%	$128.501	$128.50	$128.50	$128.50
Purchase #5	$180.93	10.446%	$199.8299	$199.83	$199.85	$199.80
Purchase #6	$11.49	9.742%	$12.6094	$12.61	$12.60	$12.60
Purchase #7	$52.36	4.391%	$54.6591	$54.66	$54.65	$54.70
7 purchase totals =	$892.88		$980.8684	$980.87	$980.85	$980.90