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	$248.65	3.672%	$257.7804	$257.78	$257.80	$257.80
Purchase #2	$126.79	10.823%	$140.5125	$140.51	$140.50	$140.50
Purchase #3	$154.88	5.178%	$162.8997	$162.90	$162.90	$162.90
Purchase #4	$151.51	9.248%	$165.5216	$165.52	$165.50	$165.50
Purchase #5	$231.89	13.694%	$263.645	$263.65	$263.65	$263.60
Purchase #6	$110.79	11.105%	$123.0932	$123.09	$123.10	$123.10
Purchase #7	$113.87	8.174%	$123.1777	$123.18	$123.20	$123.20
7 purchase totals =	$1,138.38		$1,236.6301	$1,236.63	$1,236.65	$1,236.60