Many years ago (9 to be exact, as DD is now 8) our dear old lab, Merry Puppy, ate an ENTIRE box of Lady Godiva chocolates (cellophane, cardboard and all). I had been given the box as a present, but was pregnant and very morning sick so I was saving it for "later". Darn dog had no ill effects except for some AWFUL houseclearing gas. As I stood outside getting a breath of fresh air I remember screaming at her "die you Godiva stealing dog"......we lost her in August to cancer and diabetes and the family misses her (but not her gas) terribly. Not much affected that dog's digestion- but EVERYTHING contraband made her incredibly odorous!
....we have a new golden retriever pup (okay, he will be one at the end of March, but he will always be my "baby"). He eats anything and everything, too. Thank goodness his, uhm, "gas" isn't quite so lethal. Our 5 year old rescue coon hound, on the other hand, seems to have inherited Merry Puppy's odorous production ability!
Good luck. Commercially produced sweetened chocolate is generally not too toxic. Others are correct, however, it is the unsweetened "pure" stuff that can be bad. Also shows that dog's don't taste- come on, who would willfully ingest Baker's chocolate?