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	$94.64	6.538%	$100.8276	$100.83	$100.85	$100.80
Purchase #2	$83.58	4.361%	$87.2249	$87.22	$87.20	$87.20
Purchase #3	$15.53	10.615%	$17.1785	$17.18	$17.20	$17.20
Purchase #4	$116.81	5.726%	$123.4985	$123.50	$123.50	$123.50
Purchase #5	$137.72	9.387%	$150.6478	$150.65	$150.65	$150.60
Purchase #6	$145.60	10.421%	$160.773	$160.77	$160.75	$160.80
Purchase #7	$10.43	3.324%	$10.7767	$10.78	$10.80	$10.80
7 purchase totals =	$604.31		$650.9270	$650.93	$650.95	$650.90