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	$148.48	7.639%	$159.8224	$159.82	$159.80	$159.80
Purchase #2	$45.86	10.454%	$50.6542	$50.65	$50.65	$50.70
Purchase #3	$19.52	9.158%	$21.3076	$21.31	$21.30	$21.30
Purchase #4	$61.95	5.742%	$65.5072	$65.51	$65.50	$65.50
Purchase #5	$42.72	12.429%	$48.0297	$48.03	$48.05	$48.00
Purchase #6	$172.39	13.226%	$195.1903	$195.19	$195.20	$195.20
Purchase #7	$89.77	12.443%	$100.9401	$100.94	$100.95	$100.90
7 purchase totals =	$580.69		$641.4515	$641.45	$641.45	$641.40