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	$226.60	13.236%	$256.5928	$256.59	$256.60	$256.60
Purchase #2	$217.96	10.143%	$240.0677	$240.07	$240.05	$240.10
Purchase #3	$50.25	11.417%	$55.987	$55.99	$56.00	$56.00
Purchase #4	$96.78	6.347%	$102.9226	$102.92	$102.90	$102.90
Purchase #5	$88.76	13.659%	$100.8837	$100.88	$100.90	$100.90
Purchase #6	$122.30	13.186%	$138.4265	$138.43	$138.45	$138.40
Purchase #7	$199.93	8.364%	$216.6521	$216.65	$216.65	$216.70
7 purchase totals =	$1,002.58		$1,111.5324	$1,111.53	$1,111.55	$1,111.60