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	$137.81	10.527%	$152.3173	$152.32	$152.30	$152.30
Purchase #2	$207.62	13.161%	$234.9449	$234.94	$234.95	$234.90
Purchase #3	$128.82	9.237%	$140.7191	$140.72	$140.70	$140.70
Purchase #4	$226.45	10.452%	$250.1186	$250.12	$250.10	$250.10
Purchase #5	$76.69	11.830%	$85.7624	$85.76	$85.75	$85.80
Purchase #6	$132.29	12.520%	$148.8527	$148.85	$148.85	$148.90
Purchase #7	$214.39	13.785%	$243.9437	$243.94	$243.95	$243.90
7 purchase totals =	$1,124.07		$1,256.6587	$1,256.65	$1,256.60	$1,256.60