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	$50.88	11.232%	$56.5948	$56.59	$56.60	$56.60
Purchase #2	$227.82	9.747%	$250.0256	$250.03	$250.05	$250.00
Purchase #3	$225.50	9.841%	$247.6915	$247.69	$247.70	$247.70
Purchase #4	$138.51	7.162%	$148.4301	$148.43	$148.45	$148.40
Purchase #5	$37.90	13.344%	$42.9574	$42.96	$42.95	$43.00
Purchase #6	$143.70	6.307%	$152.7632	$152.76	$152.75	$152.80
Purchase #7	$59.96	6.389%	$63.7908	$63.79	$63.80	$63.80
7 purchase totals =	$884.27		$962.2534	$962.25	$962.30	$962.30