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	$217.67	13.744%	$247.5866	$247.59	$247.60	$247.60
Purchase #2	$50.35	7.592%	$54.1726	$54.17	$54.15	$54.20
Purchase #3	$52.65	9.111%	$57.4469	$57.45	$57.45	$57.40
Purchase #4	$46.94	3.511%	$48.5881	$48.59	$48.60	$48.60
Purchase #5	$177.74	7.265%	$190.6528	$190.65	$190.65	$190.70
Purchase #6	$132.64	6.217%	$140.8862	$140.89	$140.90	$140.90
Purchase #7	$177.33	12.707%	$199.8633	$199.86	$199.85	$199.90
7 purchase totals =	$855.32		$939.1965	$939.20	$939.20	$939.30