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	$56.39	5.509%	$59.4965	$59.50	$59.50	$59.50
Purchase #2	$150.55	3.691%	$156.1068	$156.11	$156.10	$156.10
Purchase #3	$222.88	8.478%	$241.7758	$241.78	$241.80	$241.80
Purchase #4	$70.59	9.558%	$77.337	$77.34	$77.35	$77.30
Purchase #5	$18.37	3.129%	$18.9448	$18.94	$18.95	$18.90
Purchase #6	$196.69	7.246%	$210.9422	$210.94	$210.95	$210.90
Purchase #7	$210.40	6.678%	$224.4505	$224.45	$224.45	$224.50
7 purchase totals =	$925.87		$989.0536	$989.06	$989.10	$989.00