In Norway, tipping is appreciated by service staff and tips in Norway should be in the 6-10% range of your total bill.
So, if you feel you've received outstanding service, leave a nice tip. When you tip in Norwegian restaurants, you can leave your tip by rounding up the amount of the bill.
For example, if the bill for your dinner is 93.60 and you received good service, it would be appropriate for you to leave a total of 100.- in the local currency, Norwegian krone.
Note that taxi drivers may receive a tip that is a little higher. Also give this tip in form of "rounding up" to the nearest even amount (e.g. for a charge of 73.50, simply give 80.00 even).