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	$81.89	8.719%	$89.03	$89.03	$89.05	$89.00
Purchase #2	$70.78	11.324%	$78.7951	$78.80	$78.80	$78.80
Purchase #3	$227.43	12.735%	$256.3932	$256.39	$256.40	$256.40
Purchase #4	$21.42	3.457%	$22.1605	$22.16	$22.15	$22.20
Purchase #5	$26.29	6.785%	$28.0738	$28.07	$28.05	$28.10
Purchase #6	$175.29	12.666%	$197.4922	$197.49	$197.50	$197.50
Purchase #7	$33.83	13.838%	$38.5114	$38.51	$38.50	$38.50
7 purchase totals =	$636.93		$710.4562	$710.45	$710.45	$710.50