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	$179.30	6.290%	$190.578	$190.58	$190.60	$190.60
Purchase #2	$129.87	12.634%	$146.2778	$146.28	$146.30	$146.30
Purchase #3	$129.64	7.290%	$139.0908	$139.09	$139.10	$139.10
Purchase #4	$89.99	12.717%	$101.434	$101.43	$101.45	$101.40
Purchase #5	$45.51	6.613%	$48.5196	$48.52	$48.50	$48.50
Purchase #6	$111.38	13.570%	$126.4943	$126.49	$126.50	$126.50
Purchase #7	$134.80	11.308%	$150.0432	$150.04	$150.05	$150.00
7 purchase totals =	$820.49		$902.4377	$902.43	$902.50	$902.40