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	$7.29	3.367%	$7.5355	$7.54	$7.55	$7.50
Purchase #2	$121.47	8.269%	$131.5144	$131.51	$131.50	$131.50
Purchase #3	$205.40	11.103%	$228.2056	$228.21	$228.20	$228.20
Purchase #4	$131.65	6.808%	$140.6127	$140.61	$140.60	$140.60
Purchase #5	$171.50	12.437%	$192.8295	$192.83	$192.85	$192.80
Purchase #6	$38.74	4.859%	$40.6224	$40.62	$40.60	$40.60
Purchase #7	$111.80	13.446%	$126.8326	$126.83	$126.85	$126.80
7 purchase totals =	$787.85		$868.1527	$868.15	$868.15	$868.00