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	$38.61	9.628%	$42.3274	$42.33	$42.35	$42.30
Purchase #2	$34.49	9.308%	$37.7003	$37.70	$37.70	$37.70
Purchase #3	$101.34	6.232%	$107.6555	$107.66	$107.65	$107.70
Purchase #4	$63.42	10.724%	$70.2212	$70.22	$70.20	$70.20
Purchase #5	$100.64	10.332%	$111.0381	$111.04	$111.05	$111.00
Purchase #6	$170.89	4.721%	$178.9577	$178.96	$178.95	$179.00
Purchase #7	$44.56	11.333%	$49.61	$49.61	$49.60	$49.60
7 purchase totals =	$553.95		$597.5102	$597.52	$597.50	$597.50