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	$94.94	11.413%	$105.7755	$105.78	$105.80	$105.80
Purchase #2	$66.43	3.151%	$68.5232	$68.52	$68.50	$68.50
Purchase #3	$141.76	12.483%	$159.4559	$159.46	$159.45	$159.50
Purchase #4	$247.68	3.733%	$256.9259	$256.93	$256.95	$256.90
Purchase #5	$143.89	3.185%	$148.4729	$148.47	$148.45	$148.50
Purchase #6	$11.37	6.341%	$12.091	$12.09	$12.10	$12.10
Purchase #7	$101.82	13.395%	$115.4588	$115.46	$115.45	$115.50
7 purchase totals =	$807.89		$866.7032	$866.71	$866.70	$866.80