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	$48.99	13.530%	$55.6183	$55.62	$55.60	$55.60
Purchase #2	$100.29	10.492%	$110.8124	$110.81	$110.80	$110.80
Purchase #3	$6.91	8.856%	$7.5219	$7.52	$7.50	$7.50
Purchase #4	$148.38	7.256%	$159.1465	$159.15	$159.15	$159.10
Purchase #5	$159.45	8.165%	$172.4691	$172.47	$172.45	$172.50
Purchase #6	$58.67	13.729%	$66.7248	$66.72	$66.70	$66.70
Purchase #7	$156.60	4.848%	$164.192	$164.19	$164.20	$164.20
7 purchase totals =	$679.29		$736.4850	$736.48	$736.40	$736.40