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	$13.85	6.806%	$14.7926	$14.79	$14.80	$14.80
Purchase #2	$42.86	12.175%	$48.0782	$48.08	$48.10	$48.10
Purchase #3	$91.91	8.845%	$100.0394	$100.04	$100.05	$100.00
Purchase #4	$139.35	9.418%	$152.474	$152.47	$152.45	$152.50
Purchase #5	$198.57	4.808%	$208.1172	$208.12	$208.10	$208.10
Purchase #6	$64.71	3.276%	$66.8299	$66.83	$66.85	$66.80
Purchase #7	$70.77	10.585%	$78.261	$78.26	$78.25	$78.30
7 purchase totals =	$622.02		$668.5923	$668.59	$668.60	$668.60