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	$230.63	8.403%	$250.0098	$250.01	$250.00	$250.00
Purchase #2	$132.40	4.855%	$138.828	$138.83	$138.85	$138.80
Purchase #3	$107.78	9.392%	$117.9027	$117.90	$117.90	$117.90
Purchase #4	$142.26	11.491%	$158.6071	$158.61	$158.60	$158.60
Purchase #5	$146.34	12.667%	$164.8769	$164.88	$164.90	$164.90
Purchase #6	$213.66	5.724%	$225.8899	$225.89	$225.90	$225.90
Purchase #7	$210.25	5.801%	$222.4466	$222.45	$222.45	$222.40
7 purchase totals =	$1,183.32		$1,278.5610	$1,278.57	$1,278.60	$1,278.50