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	$87.59	13.393%	$99.3209	$99.32	$99.30	$99.30
Purchase #2	$125.72	8.551%	$136.4703	$136.47	$136.45	$136.50
Purchase #3	$220.27	4.189%	$229.4971	$229.50	$229.50	$229.50
Purchase #4	$58.81	6.475%	$62.6179	$62.62	$62.60	$62.60
Purchase #5	$233.84	10.575%	$258.5686	$258.57	$258.55	$258.60
Purchase #6	$66.35	12.417%	$74.5887	$74.59	$74.60	$74.60
Purchase #7	$46.87	6.297%	$49.8214	$49.82	$49.80	$49.80
7 purchase totals =	$839.45		$910.8849	$910.89	$910.80	$910.90