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	$229.86	13.176%	$260.1464	$260.15	$260.15	$260.10
Purchase #2	$37.86	4.225%	$39.4596	$39.46	$39.45	$39.50
Purchase #3	$196.74	12.523%	$221.3778	$221.38	$221.40	$221.40
Purchase #4	$82.75	8.406%	$89.706	$89.71	$89.70	$89.70
Purchase #5	$8.93	11.472%	$9.9544	$9.95	$9.95	$10.00
Purchase #6	$128.38	12.273%	$144.1361	$144.14	$144.15	$144.10
Purchase #7	$29.43	13.389%	$33.3704	$33.37	$33.35	$33.40
7 purchase totals =	$713.95		$798.1507	$798.16	$798.15	$798.20