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	$99.71	12.703%	$112.3762	$112.38	$112.40	$112.40
Purchase #2	$43.60	11.197%	$48.4819	$48.48	$48.50	$48.50
Purchase #3	$176.25	12.826%	$198.8558	$198.86	$198.85	$198.90
Purchase #4	$177.98	6.300%	$189.1927	$189.19	$189.20	$189.20
Purchase #5	$247.93	9.845%	$272.3387	$272.34	$272.35	$272.30
Purchase #6	$87.52	9.134%	$95.5141	$95.51	$95.50	$95.50
Purchase #7	$110.73	11.656%	$123.6367	$123.64	$123.65	$123.60
7 purchase totals =	$943.72		$1,040.3961	$1,040.40	$1,040.45	$1,040.40