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	$23.50	5.740%	$24.8489	$24.85	$24.85	$24.80
Purchase #2	$48.84	13.833%	$55.596	$55.60	$55.60	$55.60
Purchase #3	$39.44	3.491%	$40.8169	$40.82	$40.80	$40.80
Purchase #4	$98.69	13.200%	$111.7171	$111.72	$111.70	$111.70
Purchase #5	$94.47	13.849%	$107.5532	$107.55	$107.55	$107.60
Purchase #6	$247.32	12.485%	$278.1979	$278.20	$278.20	$278.20
Purchase #7	$64.77	3.186%	$66.8336	$66.83	$66.85	$66.80
7 purchase totals =	$617.03		$685.5636	$685.57	$685.55	$685.50