The direct answer to your direct question of "Do I pay tax for (the sale of) those 27?" is almost certainly "No."
Your per share basis of those 27 shares is the same as the per share fair market value used by your employer to calculate the compensation created by the vesting of the 67 shares, and you've already paid the tax on that compensation. So for a same day sale you expect that your per share selling price and that per share fair market value number would be more or less the same, creating a small loss due to selling commissions and fees. (Occasionally, you receive a higher per share selling price than the per share figure used by your employer, so a small taxable profit can occur. That's why I qualified by answer with "almost certainly.")
The issue you face here is that the 1099-B almost certainly has the wrong basis, though the broker should have disclosed the correct basis to use on some "supplemental information" that came with the 1099-B. Be sure you use the correct basis when you report the sale.
