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	$55.40	3.820%	$57.5163	$57.52	$57.50	$57.50
Purchase #2	$34.92	6.601%	$37.2251	$37.23	$37.25	$37.20
Purchase #3	$146.62	4.648%	$153.4349	$153.43	$153.45	$153.40
Purchase #4	$190.64	13.595%	$216.5575	$216.56	$216.55	$216.60
Purchase #5	$234.69	6.599%	$250.1772	$250.18	$250.20	$250.20
Purchase #6	$7.48	7.144%	$8.0144	$8.01	$8.00	$8.00
Purchase #7	$250.25	10.102%	$275.5303	$275.53	$275.55	$275.50
7 purchase totals =	$920.00		$998.4557	$998.46	$998.50	$998.40