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	$36.83	8.726%	$40.0438	$40.04	$40.05	$40.00
Purchase #2	$137.86	6.326%	$146.581	$146.58	$146.60	$146.60
Purchase #3	$223.80	13.428%	$253.8519	$253.85	$253.85	$253.90
Purchase #4	$60.85	11.368%	$67.7674	$67.77	$67.75	$67.80
Purchase #5	$132.89	11.709%	$148.4501	$148.45	$148.45	$148.50
Purchase #6	$114.93	13.203%	$130.1042	$130.10	$130.10	$130.10
Purchase #7	$11.48	3.319%	$11.861	$11.86	$11.85	$11.90
7 purchase totals =	$718.64		$798.6594	$798.65	$798.65	$798.80