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	$20.34	5.624%	$21.4839	$21.48	$21.50	$21.50
Purchase #2	$245.56	9.175%	$268.0901	$268.09	$268.10	$268.10
Purchase #3	$6.52	3.766%	$6.7655	$6.77	$6.75	$6.80
Purchase #4	$153.31	12.490%	$172.4584	$172.46	$172.45	$172.50
Purchase #5	$239.48	5.826%	$253.4321	$253.43	$253.45	$253.40
Purchase #6	$105.40	5.714%	$111.4226	$111.42	$111.40	$111.40
Purchase #7	$127.77	7.235%	$137.0142	$137.01	$137.00	$137.00
7 purchase totals =	$898.38		$970.6668	$970.66	$970.65	$970.70