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	$30.29	9.471%	$33.1588	$33.16	$33.15	$33.20
Purchase #2	$50.32	8.451%	$54.5725	$54.57	$54.55	$54.60
Purchase #3	$92.89	9.370%	$101.5938	$101.59	$101.60	$101.60
Purchase #4	$30.43	13.684%	$34.594	$34.59	$34.60	$34.60
Purchase #5	$241.81	12.439%	$271.8887	$271.89	$271.90	$271.90
Purchase #6	$116.63	12.345%	$131.028	$131.03	$131.05	$131.00
Purchase #7	$250.80	4.604%	$262.3468	$262.35	$262.35	$262.30
7 purchase totals =	$813.17		$889.1826	$889.18	$889.20	$889.20