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	$217.82	9.541%	$238.6022	$238.60	$238.60	$238.60
Purchase #2	$108.44	10.511%	$119.8381	$119.84	$119.85	$119.80
Purchase #3	$108.46	8.402%	$117.5728	$117.57	$117.55	$117.60
Purchase #4	$58.93	10.684%	$65.2261	$65.23	$65.25	$65.20
Purchase #5	$76.75	7.189%	$82.2676	$82.27	$82.25	$82.30
Purchase #6	$97.58	13.576%	$110.8275	$110.83	$110.85	$110.80
Purchase #7	$50.93	3.247%	$52.5837	$52.58	$52.60	$52.60
7 purchase totals =	$718.91		$786.9180	$786.92	$786.95	$786.90