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	$11.89	12.183%	$13.3386	$13.34	$13.35	$13.30
Purchase #2	$126.60	13.669%	$143.905	$143.91	$143.90	$143.90
Purchase #3	$18.90	5.436%	$19.9274	$19.93	$19.95	$19.90
Purchase #4	$81.32	13.218%	$92.0689	$92.07	$92.05	$92.10
Purchase #5	$155.99	8.305%	$168.945	$168.95	$168.95	$168.90
Purchase #6	$29.64	13.102%	$33.5234	$33.52	$33.50	$33.50
Purchase #7	$87.81	10.343%	$96.8922	$96.89	$96.90	$96.90
7 purchase totals =	$512.15		$568.6005	$568.61	$568.60	$568.50