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	$143.78	10.242%	$158.5059	$158.51	$158.50	$158.50
Purchase #2	$184.99	11.822%	$206.8595	$206.86	$206.85	$206.90
Purchase #3	$83.90	7.265%	$89.9953	$90.00	$90.00	$90.00
Purchase #4	$66.79	5.141%	$70.2237	$70.22	$70.20	$70.20
Purchase #5	$186.39	11.697%	$208.192	$208.19	$208.20	$208.20
Purchase #6	$100.88	4.792%	$105.7142	$105.71	$105.70	$105.70
Purchase #7	$208.76	12.169%	$234.164	$234.16	$234.15	$234.20
7 purchase totals =	$975.49		$1,073.6546	$1,073.65	$1,073.60	$1,073.70