banks brokers do not offer that option as far as i know, if you trade with Open Market you can.
The centre point it's a dark pool ( you can't see the volume) with any broker you can get centre point price when you buy or sell if the first inline shares come from a dark pool.
this 0.0045 means that someone it's happy to pay little more and be ahead of 0.004 as well as not moving the price.