Each order is subject to the best execution rules, which means that when being placed for execution they are routed to the exchange that gives you the best price.  This is known as NBBO (National Best Bid Offer) rule. Fractional orders are also subject to NBBO so regardless of the size you trade, you'll be getting the best price in the market at the time. 

No spread or commission is added to your order and we do not sell order flow to other market participants.