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	$217.61	3.241%	$224.6627	$224.66	$224.65	$224.70
Purchase #2	$241.59	13.842%	$275.0309	$275.03	$275.05	$275.00
Purchase #3	$38.32	13.870%	$43.635	$43.64	$43.65	$43.60
Purchase #4	$230.28	10.752%	$255.0397	$255.04	$255.05	$255.00
Purchase #5	$51.56	6.236%	$54.7753	$54.78	$54.80	$54.80
Purchase #6	$59.43	5.303%	$62.5816	$62.58	$62.60	$62.60
Purchase #7	$21.42	13.237%	$24.2554	$24.26	$24.25	$24.30
7 purchase totals =	$860.21		$939.9806	$939.99	$940.05	$940.00