No there isn't a standard amount its down to you on the service you feel provided, I would say tour guides in Russia should be considered for a tip and maybe the driver,
Tipping is a bit less common than the USA but still is a custom if you were eating then 10% would be a standard.
We did a private tour for two days in St Petersburg in 2010 with
DCL and I tipped our guide who was with us about 12 hours first day and about 8 hours on the second, I also tipped our driver. the amounts were about 10% of the cost of my private tours, plus we took our guide to lunch in the Peterhoff, that actually cost nearly nothing it is very cheap.
Tip if you can in Euros, in Russia you can tip Rubles or Euros or $, in Tallinn and Helsinki Euros, Copenhagen Kroner or Euros and Sweden Swedish kroner or Euros, if you visit Germany its Euros, and UK pounds but we do not tip a lot here.
If you are going on DCL tours then if its say 55 on a coach a small amount pp is ok, there isn't a set amount but if as said the tour guide is very good something is appreciated.
We have private tours in each port as i think that will be better than DCL and will tip about 10% in each and something for the driver if we have one.