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	$182.50	3.772%	$189.3839	$189.38	$189.40	$189.40
Purchase #2	$148.52	4.512%	$155.2212	$155.22	$155.20	$155.20
Purchase #3	$132.78	3.398%	$137.2919	$137.29	$137.30	$137.30
Purchase #4	$208.42	13.181%	$235.8918	$235.89	$235.90	$235.90
Purchase #5	$136.67	5.520%	$144.2142	$144.21	$144.20	$144.20
Purchase #6	$40.57	5.332%	$42.7332	$42.73	$42.75	$42.70
Purchase #7	$81.78	10.760%	$90.5795	$90.58	$90.60	$90.60
7 purchase totals =	$931.24		$995.3157	$995.30	$995.35	$995.30