I was just thinking about this, and thought I'd throw it out. Sub-penny pricing has been eliminated for all stocks >$1, but is still allowed for anything less. Why is $1 so magical? If a stock moves beyond the $1 range then the minimum tick size change introduces a structural break into the systems.. spiking volatility, causing havoc, etc. Seems pretty silly to me.. here is an example. Say a stock is trading at 99 cents. (1.00-0.999)/0.999= 0.0010010 So the minimum tick size is (0.1%) As soon as it reaches a dollar the minimum relative tick size is (1.00-0.99)/0.99 = ans = 0.010101 From 0.1% to 1%, the relative spread changes by an order of magnitude! This is a huge change in trading costs/risks/spread etc for no other reason than someone decided $1 was special. Now, I don't trade penny stocks so I don't really care that much, but the same problem still applies for high priced stocks.. say, google. Trading at $400 and the relative spread is as small as 0.0025%, but SIRI $5 has a minimum relative spread of 0.2%. Has anyone ever thought of the practical and economic implications of minimum sizes, scaling, stock splits, etc? This is why logarithmic charts and transformations are so popular, but it doesnt make the problem go away.