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	$228.27	12.187%	$256.0893	$256.09	$256.10	$256.10
Purchase #2	$70.32	11.339%	$78.2936	$78.29	$78.30	$78.30
Purchase #3	$59.92	9.348%	$65.5213	$65.52	$65.50	$65.50
Purchase #4	$149.61	6.760%	$159.7236	$159.72	$159.70	$159.70
Purchase #5	$87.92	12.806%	$99.179	$99.18	$99.20	$99.20
Purchase #6	$95.42	8.263%	$103.3046	$103.30	$103.30	$103.30
Purchase #7	$10.81	5.137%	$11.3653	$11.37	$11.35	$11.40
7 purchase totals =	$702.27		$773.4767	$773.47	$773.45	$773.50