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	$25.52	7.509%	$27.4363	$27.44	$27.45	$27.40
Purchase #2	$98.90	12.848%	$111.6067	$111.61	$111.60	$111.60
Purchase #3	$130.53	13.521%	$148.179	$148.18	$148.20	$148.20
Purchase #4	$81.66	7.737%	$87.978	$87.98	$88.00	$88.00
Purchase #5	$240.65	4.583%	$251.679	$251.68	$251.70	$251.70
Purchase #6	$75.25	10.709%	$83.3085	$83.31	$83.30	$83.30
Purchase #7	$152.41	13.275%	$172.6424	$172.64	$172.65	$172.60
7 purchase totals =	$804.92		$882.8299	$882.84	$882.90	$882.80