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	$183.56	3.679%	$190.3132	$190.31	$190.30	$190.30
Purchase #2	$110.78	3.628%	$114.7991	$114.80	$114.80	$114.80
Purchase #3	$159.38	5.569%	$168.2559	$168.26	$168.25	$168.30
Purchase #4	$33.39	12.193%	$37.4612	$37.46	$37.45	$37.50
Purchase #5	$52.29	8.743%	$56.8617	$56.86	$56.85	$56.90
Purchase #6	$18.95	12.164%	$21.2551	$21.26	$21.25	$21.30
Purchase #7	$14.69	3.606%	$15.2197	$15.22	$15.20	$15.20
7 purchase totals =	$573.04		$604.1659	$604.17	$604.10	$604.30