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	$37.57	4.226%	$39.1577	$39.16	$39.15	$39.20
Purchase #2	$236.35	3.603%	$244.8657	$244.87	$244.85	$244.90
Purchase #3	$107.97	11.399%	$120.2775	$120.28	$120.30	$120.30
Purchase #4	$28.78	9.140%	$31.4105	$31.41	$31.40	$31.40
Purchase #5	$80.27	12.272%	$90.1207	$90.12	$90.10	$90.10
Purchase #6	$100.89	3.368%	$104.288	$104.29	$104.30	$104.30
Purchase #7	$13.47	11.329%	$14.996	$15.00	$15.00	$15.00
7 purchase totals =	$605.30		$645.1161	$645.13	$645.10	$645.20