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	$12.66	6.673%	$13.5048	$13.50	$13.50	$13.50
Purchase #2	$93.57	10.715%	$103.596	$103.60	$103.60	$103.60
Purchase #3	$100.57	3.119%	$103.7068	$103.71	$103.70	$103.70
Purchase #4	$21.62	7.353%	$23.2097	$23.21	$23.20	$23.20
Purchase #5	$24.54	4.337%	$25.6043	$25.60	$25.60	$25.60
Purchase #6	$160.72	9.824%	$176.5091	$176.51	$176.50	$176.50
Purchase #7	$109.84	3.566%	$113.7569	$113.76	$113.75	$113.80
7 purchase totals =	$523.52		$559.8876	$559.89	$559.85	$559.90