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	$124.61	13.473%	$141.3987	$141.40	$141.40	$141.40
Purchase #2	$84.26	4.516%	$88.0652	$88.07	$88.05	$88.10
Purchase #3	$24.46	9.227%	$26.7169	$26.72	$26.70	$26.70
Purchase #4	$54.57	12.622%	$61.4578	$61.46	$61.45	$61.50
Purchase #5	$200.27	11.174%	$222.6482	$222.65	$222.65	$222.60
Purchase #6	$236.97	5.602%	$250.2451	$250.25	$250.25	$250.20
Purchase #7	$37.76	7.828%	$40.7159	$40.72	$40.70	$40.70
7 purchase totals =	$762.90		$831.2478	$831.27	$831.20	$831.20