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	$229.43	11.365%	$255.5047	$255.50	$255.50	$255.50
Purchase #2	$50.44	7.798%	$54.3733	$54.37	$54.35	$54.40
Purchase #3	$93.89	8.538%	$101.9063	$101.91	$101.90	$101.90
Purchase #4	$42.92	5.490%	$45.2763	$45.28	$45.30	$45.30
Purchase #5	$18.79	3.717%	$19.4884	$19.49	$19.50	$19.50
Purchase #6	$148.58	8.659%	$161.4455	$161.45	$161.45	$161.40
Purchase #7	$21.59	13.504%	$24.5055	$24.51	$24.50	$24.50
7 purchase totals =	$605.64		$662.5000	$662.51	$662.50	$662.50