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	$88.32	12.545%	$99.3997	$99.40	$99.40	$99.40
Purchase #2	$117.41	12.864%	$132.5136	$132.51	$132.50	$132.50
Purchase #3	$11.42	12.789%	$12.8805	$12.88	$12.90	$12.90
Purchase #4	$141.56	13.666%	$160.9056	$160.91	$160.90	$160.90
Purchase #5	$234.38	3.193%	$241.8638	$241.86	$241.85	$241.90
Purchase #6	$80.43	8.551%	$87.3076	$87.31	$87.30	$87.30
Purchase #7	$171.86	8.825%	$187.0266	$187.03	$187.05	$187.00
7 purchase totals =	$845.38		$921.8974	$921.90	$921.90	$921.90