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	$40.31	5.698%	$42.6069	$42.61	$42.60	$42.60
Purchase #2	$53.78	11.509%	$59.9695	$59.97	$59.95	$60.00
Purchase #3	$121.72	10.248%	$134.1939	$134.19	$134.20	$134.20
Purchase #4	$38.57	4.172%	$40.1791	$40.18	$40.20	$40.20
Purchase #5	$103.89	13.288%	$117.6949	$117.69	$117.70	$117.70
Purchase #6	$176.31	8.298%	$190.9402	$190.94	$190.95	$190.90
Purchase #7	$204.94	10.749%	$226.969	$226.97	$226.95	$227.00
7 purchase totals =	$739.52		$812.5535	$812.55	$812.55	$812.60