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	$37.95	10.683%	$42.0042	$42.00	$42.00	$42.00
Purchase #2	$111.67	13.358%	$126.5869	$126.59	$126.60	$126.60
Purchase #3	$60.57	8.811%	$65.9068	$65.91	$65.90	$65.90
Purchase #4	$78.38	12.703%	$88.3366	$88.34	$88.35	$88.30
Purchase #5	$108.89	12.508%	$122.51	$122.51	$122.50	$122.50
Purchase #6	$77.95	13.333%	$88.3431	$88.34	$88.35	$88.30
Purchase #7	$161.27	7.242%	$172.9492	$172.95	$172.95	$172.90
7 purchase totals =	$636.68		$706.6368	$706.64	$706.65	$706.50