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	$102.60	13.523%	$116.4746	$116.47	$116.45	$116.50
Purchase #2	$74.57	11.357%	$83.0389	$83.04	$83.05	$83.00
Purchase #3	$56.99	4.250%	$59.4121	$59.41	$59.40	$59.40
Purchase #4	$112.26	3.676%	$116.3867	$116.39	$116.40	$116.40
Purchase #5	$170.43	11.724%	$190.4112	$190.41	$190.40	$190.40
Purchase #6	$122.31	11.825%	$136.7732	$136.77	$136.75	$136.80
Purchase #7	$192.83	13.569%	$218.9951	$219.00	$219.00	$219.00
7 purchase totals =	$831.99		$921.4918	$921.49	$921.45	$921.50