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	$33.93	13.136%	$38.387	$38.39	$38.40	$38.40
Purchase #2	$141.72	3.140%	$146.17	$146.17	$146.15	$146.20
Purchase #3	$118.72	6.784%	$126.774	$126.77	$126.75	$126.80
Purchase #4	$129.28	7.634%	$139.1492	$139.15	$139.15	$139.10
Purchase #5	$169.99	12.413%	$191.0909	$191.09	$191.10	$191.10
Purchase #6	$101.42	9.481%	$111.0356	$111.04	$111.05	$111.00
Purchase #7	$83.52	10.767%	$92.5126	$92.51	$92.50	$92.50
7 purchase totals =	$778.58		$845.1193	$845.12	$845.10	$845.10