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	$108.57	8.528%	$117.8288	$117.83	$117.85	$117.80
Purchase #2	$192.75	11.693%	$215.2883	$215.29	$215.30	$215.30
Purchase #3	$179.38	6.205%	$190.5105	$190.51	$190.50	$190.50
Purchase #4	$102.69	8.526%	$111.4453	$111.45	$111.45	$111.40
Purchase #5	$133.29	7.846%	$143.7479	$143.75	$143.75	$143.70
Purchase #6	$247.50	3.273%	$255.6007	$255.60	$255.60	$255.60
Purchase #7	$176.68	3.571%	$182.9892	$182.99	$183.00	$183.00
7 purchase totals =	$1,140.86		$1,217.4107	$1,217.42	$1,217.45	$1,217.30