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	$83.26	8.723%	$90.5228	$90.52	$90.50	$90.50
Purchase #2	$53.57	7.648%	$57.667	$57.67	$57.65	$57.70
Purchase #3	$227.29	3.655%	$235.5974	$235.60	$235.60	$235.60
Purchase #4	$137.89	11.589%	$153.8701	$153.87	$153.85	$153.90
Purchase #5	$148.56	11.457%	$165.5805	$165.58	$165.60	$165.60
Purchase #6	$45.71	5.578%	$48.2597	$48.26	$48.25	$48.30
Purchase #7	$134.80	11.417%	$150.1901	$150.19	$150.20	$150.20
7 purchase totals =	$831.08		$901.6876	$901.69	$901.65	$901.80