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	$99.70	4.182%	$103.8695	$103.87	$103.85	$103.90
Purchase #2	$90.51	7.852%	$97.6168	$97.62	$97.60	$97.60
Purchase #3	$38.74	9.604%	$42.4606	$42.46	$42.45	$42.50
Purchase #4	$114.60	7.509%	$123.2053	$123.21	$123.20	$123.20
Purchase #5	$147.38	12.340%	$165.5667	$165.57	$165.55	$165.60
Purchase #6	$12.86	6.262%	$13.6653	$13.67	$13.65	$13.70
Purchase #7	$113.70	6.837%	$121.4737	$121.47	$121.45	$121.50
7 purchase totals =	$617.49		$667.8579	$667.87	$667.75	$668.00