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	$136.74	4.675%	$143.1326	$143.13	$143.15	$143.10
Purchase #2	$124.68	5.738%	$131.8341	$131.83	$131.85	$131.80
Purchase #3	$225.96	13.517%	$256.503	$256.50	$256.50	$256.50
Purchase #4	$157.59	9.654%	$172.8037	$172.80	$172.80	$172.80
Purchase #5	$103.60	13.787%	$117.8833	$117.88	$117.90	$117.90
Purchase #6	$113.85	11.447%	$126.8824	$126.88	$126.90	$126.90
Purchase #7	$7.72	4.847%	$8.0942	$8.09	$8.10	$8.10
7 purchase totals =	$870.14		$957.1333	$957.11	$957.20	$957.10