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	$103.57	12.105%	$116.1071	$116.11	$116.10	$116.10
Purchase #2	$85.76	5.561%	$90.5291	$90.53	$90.55	$90.50
Purchase #3	$35.90	8.371%	$38.9052	$38.91	$38.90	$38.90
Purchase #4	$82.81	3.724%	$85.8938	$85.89	$85.90	$85.90
Purchase #5	$48.98	5.344%	$51.5975	$51.60	$51.60	$51.60
Purchase #6	$51.39	5.399%	$54.1645	$54.16	$54.15	$54.20
Purchase #7	$104.51	13.836%	$118.97	$118.97	$118.95	$119.00
7 purchase totals =	$512.92		$556.1672	$556.17	$556.15	$556.20