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	$11.31	7.511%	$12.1595	$12.16	$12.15	$12.20
Purchase #2	$190.55	5.266%	$200.5844	$200.58	$200.60	$200.60
Purchase #3	$80.73	3.346%	$83.4312	$83.43	$83.45	$83.40
Purchase #4	$52.89	8.733%	$57.5089	$57.51	$57.50	$57.50
Purchase #5	$11.59	11.734%	$12.95	$12.95	$12.95	$13.00
Purchase #6	$79.64	13.761%	$90.5993	$90.60	$90.60	$90.60
Purchase #7	$145.47	10.526%	$160.7822	$160.78	$160.80	$160.80
7 purchase totals =	$572.18		$618.0155	$618.01	$618.05	$618.10