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	$39.80	7.690%	$42.8606	$42.86	$42.85	$42.90
Purchase #2	$143.51	3.738%	$148.8744	$148.87	$148.85	$148.90
Purchase #3	$35.70	9.648%	$39.1443	$39.14	$39.15	$39.10
Purchase #4	$148.63	6.310%	$158.0086	$158.01	$158.00	$158.00
Purchase #5	$9.47	9.376%	$10.3579	$10.36	$10.35	$10.40
Purchase #6	$48.60	5.741%	$51.3901	$51.39	$51.40	$51.40
Purchase #7	$110.98	6.229%	$117.8929	$117.89	$117.90	$117.90
7 purchase totals =	$536.69		$568.5288	$568.52	$568.50	$568.60