As I read the information on the relevant website,
http://www.vr.fi/heo/eng/index.html
VR don't seem to offer return fares,
per se. i.e. return journeys are booked as two singles, in the same way that budget airlines price their tickets.
Your fares would seem to be �75.30, in each direction, irrespective of whether you use Rovaniemi or Tikkurila station.
For most European rail travel, I usually recommend speaking to the UK office of Deutche Bahn (which sells tickets on behalf of most European rail operators). VR's information page confirms that DB is one of their accredited agents in the UK:
http://www.vr.fi/heo/eng/palvelut/finformation .htm
So, if you phone DB on 08718 80 80 66, you can speak to someone who'll be able to give you definitive information about whether return tickets are available on VR services, and also able to take your booking.
Chris