The gp =/= GP issue is actually symptomatic of a larger issue relating to currency conversion. Yes, we all know that 1gp is the same as 1GP, but to a computer they are as different as $1 being the same/different as 1gp.
I am working (slowly) on a new Extension (called the DOE: WMC - Weights, Measurements & Currencies) that will solve this issue and thus all the issues around currency-conversion, giving change, etc - but I kept getting dragged off onto other things that other people want done "now".
The rounding issue is also being worked on - its an issue with the way computers store fractional numbers, and thus integral to the FG Engine. Still, we'll see what we can do.
TL;DR: its coming, but people are just going to have to be patient - I'm only one guy and there's only 24 hours in a day (and, for the record, my health isn't 100% at the moment - my issue, but it effects my productivity :( ).