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	$145.63	12.335%	$163.5935	$163.59	$163.60	$163.60
Purchase #2	$37.78	12.859%	$42.6381	$42.64	$42.65	$42.60
Purchase #3	$124.74	10.595%	$137.9562	$137.96	$137.95	$138.00
Purchase #4	$213.74	6.536%	$227.71	$227.71	$227.70	$227.70
Purchase #5	$42.62	6.452%	$45.3698	$45.37	$45.35	$45.40
Purchase #6	$221.88	8.286%	$240.265	$240.27	$240.25	$240.30
Purchase #7	$105.99	5.208%	$111.51	$111.51	$111.50	$111.50
7 purchase totals =	$892.38		$969.0426	$969.05	$969.00	$969.10