Sotek: Either way, the market will reach equilibrium. the difference is the speed at which it will happen. The more frequent the undercutting, the faster it will reach it. Also to show you how and why including more tax would negatively effect the market, here is a graph for you:
http://ingrimayne.com/econ/government/Figure13.4.gif
the big triangle between ab&c is the dead weight loss, which is a loss of efficiency within the market. The more of a tax you impose, the larger the triangle and the less efficient the market becomes. (shaded regions are the tax revenue which is gil taken out of the game). Notice how the supply line shifts left the more and greater the tax becomes, and now look what happens to the price increase, and quantity supplied decreases as the line continues to shift left.