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	$77.92	7.636%	$83.87	$83.87	$83.85	$83.90
Purchase #2	$83.96	7.104%	$89.9245	$89.92	$89.90	$89.90
Purchase #3	$242.38	5.624%	$256.0115	$256.01	$256.00	$256.00
Purchase #4	$97.82	4.526%	$102.2473	$102.25	$102.25	$102.20
Purchase #5	$117.87	12.814%	$132.9739	$132.97	$132.95	$133.00
Purchase #6	$9.88	5.863%	$10.4593	$10.46	$10.45	$10.50
Purchase #7	$20.73	3.340%	$21.4224	$21.42	$21.40	$21.40
7 purchase totals =	$650.56		$696.9089	$696.90	$696.80	$696.90