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	$237.77	6.176%	$252.4547	$252.45	$252.45	$252.50
Purchase #2	$84.88	5.826%	$89.8251	$89.83	$89.85	$89.80
Purchase #3	$234.41	13.443%	$265.9217	$265.92	$265.90	$265.90
Purchase #4	$53.36	11.339%	$59.4105	$59.41	$59.40	$59.40
Purchase #5	$191.94	8.460%	$208.1781	$208.18	$208.20	$208.20
Purchase #6	$130.80	13.563%	$148.5404	$148.54	$148.55	$148.50
Purchase #7	$111.29	7.531%	$119.6712	$119.67	$119.65	$119.70
7 purchase totals =	$1,044.45		$1,144.0017	$1,144.00	$1,144.00	$1,144.00