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	$37.86	11.378%	$42.1677	$42.17	$42.15	$42.20
Purchase #2	$16.64	13.577%	$18.8992	$18.90	$18.90	$18.90
Purchase #3	$19.46	9.385%	$21.2863	$21.29	$21.30	$21.30
Purchase #4	$145.81	10.820%	$161.5866	$161.59	$161.60	$161.60
Purchase #5	$138.46	6.390%	$147.3076	$147.31	$147.30	$147.30
Purchase #6	$20.60	13.261%	$23.3318	$23.33	$23.35	$23.30
Purchase #7	$155.83	10.143%	$171.6358	$171.64	$171.65	$171.60
7 purchase totals =	$534.66		$586.2150	$586.23	$586.25	$586.20