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	$239.90	13.628%	$272.5936	$272.59	$272.60	$272.60
Purchase #2	$34.59	13.832%	$39.3745	$39.37	$39.35	$39.40
Purchase #3	$243.70	13.152%	$275.7514	$275.75	$275.75	$275.80
Purchase #4	$97.78	12.847%	$110.3418	$110.34	$110.35	$110.30
Purchase #5	$69.56	11.434%	$77.5135	$77.51	$77.50	$77.50
Purchase #6	$109.56	13.603%	$124.4634	$124.46	$124.45	$124.50
Purchase #7	$56.60	4.703%	$59.2619	$59.26	$59.25	$59.30
7 purchase totals =	$851.69		$959.3001	$959.28	$959.25	$959.40