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	$120.89	13.705%	$137.458	$137.46	$137.45	$137.50
Purchase #2	$116.49	13.193%	$131.8585	$131.86	$131.85	$131.90
Purchase #3	$144.58	9.833%	$158.7966	$158.80	$158.80	$158.80
Purchase #4	$123.82	4.151%	$128.9598	$128.96	$128.95	$129.00
Purchase #5	$51.37	10.754%	$56.8943	$56.89	$56.90	$56.90
Purchase #6	$52.36	8.124%	$56.6137	$56.61	$56.60	$56.60
Purchase #7	$16.72	4.367%	$17.4502	$17.45	$17.45	$17.50
7 purchase totals =	$626.23		$688.0311	$688.03	$688.00	$688.20