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	$81.82	9.403%	$89.5135	$89.51	$89.50	$89.50
Purchase #2	$7.85	12.618%	$8.8405	$8.84	$8.85	$8.80
Purchase #3	$138.39	7.314%	$148.5118	$148.51	$148.50	$148.50
Purchase #4	$157.90	12.785%	$178.0875	$178.09	$178.10	$178.10
Purchase #5	$146.77	8.673%	$159.4994	$159.50	$159.50	$159.50
Purchase #6	$62.50	13.128%	$70.705	$70.71	$70.70	$70.70
Purchase #7	$137.68	10.767%	$152.504	$152.50	$152.50	$152.50
7 purchase totals =	$732.91		$807.6617	$807.66	$807.65	$807.60