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	$10.58	9.581%	$11.5937	$11.59	$11.60	$11.60
Purchase #2	$108.42	4.388%	$113.1775	$113.18	$113.20	$113.20
Purchase #3	$100.56	12.380%	$113.0093	$113.01	$113.00	$113.00
Purchase #4	$22.61	8.864%	$24.6142	$24.61	$24.60	$24.60
Purchase #5	$144.59	7.786%	$155.8478	$155.85	$155.85	$155.80
Purchase #6	$229.91	13.252%	$260.3777	$260.38	$260.40	$260.40
Purchase #7	$79.42	13.533%	$90.1679	$90.17	$90.15	$90.20
7 purchase totals =	$696.09		$768.7881	$768.79	$768.80	$768.80