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	$42.51	5.839%	$44.9922	$44.99	$45.00	$45.00
Purchase #2	$128.34	11.597%	$143.2236	$143.22	$143.20	$143.20
Purchase #3	$118.32	7.775%	$127.5194	$127.52	$127.50	$127.50
Purchase #4	$110.31	8.677%	$119.8816	$119.88	$119.90	$119.90
Purchase #5	$246.83	13.874%	$281.0752	$281.08	$281.10	$281.10
Purchase #6	$98.62	12.575%	$111.0215	$111.02	$111.00	$111.00
Purchase #7	$157.31	4.768%	$164.8105	$164.81	$164.80	$164.80
7 purchase totals =	$902.24		$992.5240	$992.52	$992.50	$992.50