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	$141.73	9.425%	$155.0881	$155.09	$155.10	$155.10
Purchase #2	$205.32	3.674%	$212.8635	$212.86	$212.85	$212.90
Purchase #3	$159.76	11.801%	$178.6133	$178.61	$178.60	$178.60
Purchase #4	$105.33	5.827%	$111.4676	$111.47	$111.45	$111.50
Purchase #5	$221.26	9.252%	$241.731	$241.73	$241.75	$241.70
Purchase #6	$111.52	13.562%	$126.6443	$126.64	$126.65	$126.60
Purchase #7	$247.98	12.724%	$279.533	$279.53	$279.55	$279.50
7 purchase totals =	$1,192.90		$1,305.9408	$1,305.93	$1,305.95	$1,305.90