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	$132.59	4.540%	$138.6096	$138.61	$138.60	$138.60
Purchase #2	$186.58	12.480%	$209.8652	$209.87	$209.85	$209.90
Purchase #3	$115.78	10.221%	$127.6139	$127.61	$127.60	$127.60
Purchase #4	$37.92	11.840%	$42.4097	$42.41	$42.40	$42.40
Purchase #5	$78.37	3.256%	$80.9217	$80.92	$80.90	$80.90
Purchase #6	$168.81	4.563%	$176.5128	$176.51	$176.50	$176.50
Purchase #7	$198.38	5.678%	$209.644	$209.64	$209.65	$209.60
7 purchase totals =	$918.43		$985.5769	$985.57	$985.50	$985.50