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	$152.73	4.420%	$159.4807	$159.48	$159.50	$159.50
Purchase #2	$53.94	4.684%	$56.4665	$56.47	$56.45	$56.50
Purchase #3	$50.48	9.564%	$55.3079	$55.31	$55.30	$55.30
Purchase #4	$94.89	10.749%	$105.0897	$105.09	$105.10	$105.10
Purchase #5	$222.74	8.413%	$241.4791	$241.48	$241.50	$241.50
Purchase #6	$18.75	13.530%	$21.2869	$21.29	$21.30	$21.30
Purchase #7	$9.78	5.388%	$10.3069	$10.31	$10.30	$10.30
7 purchase totals =	$603.31		$649.4177	$649.43	$649.45	$649.50