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	$42.50	13.149%	$48.0883	$48.09	$48.10	$48.10
Purchase #2	$131.69	10.326%	$145.2883	$145.29	$145.30	$145.30
Purchase #3	$152.59	3.445%	$157.8467	$157.85	$157.85	$157.80
Purchase #4	$143.78	10.549%	$158.9474	$158.95	$158.95	$158.90
Purchase #5	$124.78	6.605%	$133.0217	$133.02	$133.00	$133.00
Purchase #6	$151.67	8.852%	$165.0958	$165.10	$165.10	$165.10
Purchase #7	$57.88	5.769%	$61.2191	$61.22	$61.20	$61.20
7 purchase totals =	$804.89		$869.5073	$869.52	$869.50	$869.40