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	$34.90	11.362%	$38.8653	$38.87	$38.85	$38.90
Purchase #2	$146.32	12.374%	$164.4256	$164.43	$164.45	$164.40
Purchase #3	$126.84	13.257%	$143.6552	$143.66	$143.65	$143.70
Purchase #4	$47.32	3.786%	$49.1115	$49.11	$49.10	$49.10
Purchase #5	$142.55	7.691%	$153.5135	$153.51	$153.50	$153.50
Purchase #6	$117.86	4.874%	$123.6045	$123.60	$123.60	$123.60
Purchase #7	$196.89	10.249%	$217.0693	$217.07	$217.05	$217.10
7 purchase totals =	$812.68		$890.2449	$890.25	$890.20	$890.30