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	$98.39	6.126%	$104.4174	$104.42	$104.40	$104.40
Purchase #2	$104.81	12.219%	$117.6167	$117.62	$117.60	$117.60
Purchase #3	$97.43	3.208%	$100.5556	$100.56	$100.55	$100.60
Purchase #4	$90.93	8.724%	$98.8627	$98.86	$98.85	$98.90
Purchase #5	$97.44	9.677%	$106.8693	$106.87	$106.85	$106.90
Purchase #6	$67.33	13.874%	$76.6714	$76.67	$76.65	$76.70
Purchase #7	$149.90	4.328%	$156.3877	$156.39	$156.40	$156.40
7 purchase totals =	$706.23		$761.3808	$761.39	$761.30	$761.50