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	$35.60	10.689%	$39.4053	$39.41	$39.40	$39.40
Purchase #2	$101.52	3.821%	$105.3991	$105.40	$105.40	$105.40
Purchase #3	$133.83	12.401%	$150.4263	$150.43	$150.45	$150.40
Purchase #4	$132.59	5.270%	$139.5775	$139.58	$139.60	$139.60
Purchase #5	$23.81	11.628%	$26.5786	$26.58	$26.60	$26.60
Purchase #6	$78.93	12.577%	$88.857	$88.86	$88.85	$88.90
Purchase #7	$107.62	13.513%	$122.1627	$122.16	$122.15	$122.20
7 purchase totals =	$613.90		$672.4065	$672.42	$672.45	$672.50