Hello again and thanks for waiting.
I have worked out an answer for you, please read it through and see what you think, I can make the following general comments based on my past experience of just such cases over the years :
1. The botXXXXX XXXXXne is this, while grapes can be very toxic to dogs but they usually have to eat a fair number before they will be seriously affected, more than your dog ate.
The ASPCA Animal Poison Control Center studies suggest that the lowest documented toxic grape dose for dogs is 0.1 oz/kg and this equals around 10 to 12 grapes in a 20 pound dog. Going on this your dog should be fine.
You can check this information HERE
2. Grape toxicity is a strange toxin though and is little understood some dogs only eat a relatively small amount and have problems, but others can eat lots and suffer no ill effects, but as I said your dog should be fine. Read the symptoms etc. HERE
3. You should however try and limit your dog's access to grapes in the future as much as possible though.
I hope I have covered your question fully enough but if you would like further clarification or to talk things over a bit more then I will be on-line for the next hour or so and I will be more than pleased to continue working with you.