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	$221.30	5.528%	$233.5335	$233.53	$233.55	$233.50
Purchase #2	$49.29	9.331%	$53.8892	$53.89	$53.90	$53.90
Purchase #3	$136.31	5.510%	$143.8207	$143.82	$143.80	$143.80
Purchase #4	$116.64	8.817%	$126.9241	$126.92	$126.90	$126.90
Purchase #5	$111.90	4.517%	$116.9545	$116.95	$116.95	$117.00
Purchase #6	$63.27	5.404%	$66.6891	$66.69	$66.70	$66.70
Purchase #7	$240.51	6.699%	$256.6218	$256.62	$256.60	$256.60
7 purchase totals =	$939.22		$998.4329	$998.42	$998.40	$998.40