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	$152.28	8.653%	$165.4568	$165.46	$165.45	$165.50
Purchase #2	$77.49	12.502%	$87.1778	$87.18	$87.20	$87.20
Purchase #3	$249.88	12.114%	$280.1505	$280.15	$280.15	$280.20
Purchase #4	$64.95	10.403%	$71.7067	$71.71	$71.70	$71.70
Purchase #5	$103.78	12.545%	$116.7992	$116.80	$116.80	$116.80
Purchase #6	$125.34	4.340%	$130.7798	$130.78	$130.80	$130.80
Purchase #7	$55.89	12.213%	$62.7158	$62.72	$62.70	$62.70
7 purchase totals =	$829.61		$914.7866	$914.80	$914.80	$914.90