In Europe they do not tip like they do in the US! Tips are typically not expected by Europeans, however, they also do know that Americans do tip and so they may expect something. As always, tipping is completely up to you!
Suggested tipping amounts:
Restaurant service: Please check your bill as sometimes they add a service charge. This would be the tip. If no service charge is added, then rounding up or 10% is completely acceptable. No need for 15-20+% like in the US! They are paid a higher wage and do not live on mostly tips in most European countries.
Baggage service: This is similar to the US around $1 or Euro per bag.
Tour guides: $5 or Euro per person for half day tours. $10 or Euro per person for full day tours. Groups and private can be adjusted as needed.
A token small tip for a driver is also appreciated but not necessary!
You can tip in any currency since it is a gift! Many Europeans are used to accepting tips in USD.