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	$11.61	7.259%	$12.4528	$12.45	$12.45	$12.50
Purchase #2	$199.61	4.314%	$208.2212	$208.22	$208.20	$208.20
Purchase #3	$110.39	8.341%	$119.5976	$119.60	$119.60	$119.60
Purchase #4	$163.46	13.110%	$184.8896	$184.89	$184.90	$184.90
Purchase #5	$40.43	8.257%	$43.7683	$43.77	$43.75	$43.80
Purchase #6	$196.91	5.873%	$208.4745	$208.47	$208.45	$208.50
Purchase #7	$209.43	10.427%	$231.2673	$231.27	$231.25	$231.30
7 purchase totals =	$931.84		$1,008.6713	$1,008.67	$1,008.60	$1,008.80