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	$77.65	8.187%	$84.0072	$84.01	$84.00	$84.00
Purchase #2	$150.34	10.747%	$166.497	$166.50	$166.50	$166.50
Purchase #3	$141.37	6.184%	$150.1123	$150.11	$150.10	$150.10
Purchase #4	$85.60	5.761%	$90.5314	$90.53	$90.55	$90.50
Purchase #5	$76.83	11.754%	$85.8606	$85.86	$85.85	$85.90
Purchase #6	$33.43	4.262%	$34.8548	$34.85	$34.85	$34.90
Purchase #7	$52.44	4.108%	$54.5942	$54.59	$54.60	$54.60
7 purchase totals =	$617.66		$666.4575	$666.45	$666.45	$666.50