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	$48.86	11.712%	$54.5825	$54.58	$54.60	$54.60
Purchase #2	$51.90	4.556%	$54.2646	$54.26	$54.25	$54.30
Purchase #3	$217.47	7.485%	$233.7476	$233.75	$233.75	$233.70
Purchase #4	$6.91	10.563%	$7.6399	$7.64	$7.65	$7.60
Purchase #5	$11.62	9.853%	$12.7649	$12.76	$12.75	$12.80
Purchase #6	$131.34	13.189%	$148.6624	$148.66	$148.65	$148.70
Purchase #7	$100.66	10.384%	$111.1125	$111.11	$111.10	$111.10
7 purchase totals =	$568.76		$622.7744	$622.76	$622.75	$622.80