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	$43.28	12.140%	$48.5342	$48.53	$48.55	$48.50
Purchase #2	$172.54	3.806%	$179.1069	$179.11	$179.10	$179.10
Purchase #3	$216.42	11.628%	$241.5853	$241.59	$241.60	$241.60
Purchase #4	$139.55	3.569%	$144.5305	$144.53	$144.55	$144.50
Purchase #5	$174.65	7.217%	$187.2545	$187.25	$187.25	$187.30
Purchase #6	$241.79	7.334%	$259.5229	$259.52	$259.50	$259.50
Purchase #7	$247.32	3.106%	$255.0018	$255.00	$255.00	$255.00
7 purchase totals =	$1,235.55		$1,315.5361	$1,315.53	$1,315.55	$1,315.50