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	$37.84	4.509%	$39.5462	$39.55	$39.55	$39.50
Purchase #2	$234.74	11.624%	$262.0262	$262.03	$262.05	$262.00
Purchase #3	$108.35	11.677%	$121.002	$121.00	$121.00	$121.00
Purchase #4	$131.61	8.182%	$142.3783	$142.38	$142.40	$142.40
Purchase #5	$103.67	7.565%	$111.5126	$111.51	$111.50	$111.50
Purchase #6	$34.97	7.709%	$37.6658	$37.67	$37.65	$37.70
Purchase #7	$108.25	3.248%	$111.766	$111.77	$111.75	$111.80
7 purchase totals =	$759.43		$825.8971	$825.91	$825.90	$825.90