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	$52.80	8.457%	$57.2653	$57.27	$57.25	$57.30
Purchase #2	$146.83	11.784%	$164.1324	$164.13	$164.15	$164.10
Purchase #3	$245.67	3.358%	$253.9196	$253.92	$253.90	$253.90
Purchase #4	$90.41	12.863%	$102.0394	$102.04	$102.05	$102.00
Purchase #5	$220.64	7.314%	$236.7776	$236.78	$236.80	$236.80
Purchase #6	$101.43	10.232%	$111.8083	$111.81	$111.80	$111.80
Purchase #7	$29.34	7.872%	$31.6496	$31.65	$31.65	$31.60
7 purchase totals =	$887.12		$957.5922	$957.60	$957.60	$957.50