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	$25.71	13.541%	$29.1914	$29.19	$29.20	$29.20
Purchase #2	$189.41	5.536%	$199.8957	$199.90	$199.90	$199.90
Purchase #3	$55.61	9.530%	$60.9096	$60.91	$60.90	$60.90
Purchase #4	$100.65	10.808%	$111.5283	$111.53	$111.55	$111.50
Purchase #5	$243.40	4.261%	$253.7713	$253.77	$253.75	$253.80
Purchase #6	$64.81	12.189%	$72.7097	$72.71	$72.70	$72.70
Purchase #7	$234.40	5.205%	$246.6005	$246.60	$246.60	$246.60
7 purchase totals =	$913.99		$974.6065	$974.61	$974.60	$974.60