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	$124.91	12.631%	$140.6874	$140.69	$140.70	$140.70
Purchase #2	$39.85	5.724%	$42.131	$42.13	$42.15	$42.10
Purchase #3	$11.26	5.776%	$11.9104	$11.91	$11.90	$11.90
Purchase #4	$159.38	11.544%	$177.7788	$177.78	$177.80	$177.80
Purchase #5	$97.63	13.792%	$111.0951	$111.10	$111.10	$111.10
Purchase #6	$73.69	13.713%	$83.7951	$83.80	$83.80	$83.80
Purchase #7	$134.87	12.554%	$151.8016	$151.80	$151.80	$151.80
7 purchase totals =	$641.59		$719.1994	$719.21	$719.25	$719.20