OT - Pawsy I know lowtrades doesn't charge you extra commission if you get filled on one order over multiple days. There are other fees though. The commission is 4.95 per trade but there are extra fees when you sell so it is around 15 dollars round trip. If you want to buy 500K or more stock they will charge you a block trading fee of 1 percent of your order amount. They also charge you an inactivity fee every 6 months by accident (I know yeah right) that you have to call in about to get removed.
Pawsy - the same thing has happened to me in the past with Scottrade, so now I always click aon (all or none). It doesn't seem to have an effect getting all the shares I want. Their policy is you won't be charged an extra commission if the fills take place in the same day, just if it carries over into subsequent days.