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	$241.75	6.105%	$256.5088	$256.51	$256.50	$256.50
Purchase #2	$229.35	5.172%	$241.212	$241.21	$241.20	$241.20
Purchase #3	$47.50	6.717%	$50.6906	$50.69	$50.70	$50.70
Purchase #4	$198.77	11.593%	$221.8134	$221.81	$221.80	$221.80
Purchase #5	$228.92	6.209%	$243.1336	$243.13	$243.15	$243.10
Purchase #6	$13.38	5.148%	$14.0688	$14.07	$14.05	$14.10
Purchase #7	$172.58	7.250%	$185.0921	$185.09	$185.10	$185.10
7 purchase totals =	$1,132.25		$1,212.5193	$1,212.51	$1,212.50	$1,212.50