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	$41.47	9.836%	$45.549	$45.55	$45.55	$45.50
Purchase #2	$119.71	13.619%	$136.0133	$136.01	$136.00	$136.00
Purchase #3	$103.46	4.863%	$108.4913	$108.49	$108.50	$108.50
Purchase #4	$102.63	8.437%	$111.2889	$111.29	$111.30	$111.30
Purchase #5	$5.60	11.595%	$6.2493	$6.25	$6.25	$6.20
Purchase #6	$45.48	12.874%	$51.3351	$51.34	$51.35	$51.30
Purchase #7	$78.46	6.403%	$83.4838	$83.48	$83.50	$83.50
7 purchase totals =	$496.81		$542.4107	$542.41	$542.45	$542.30