Tomorrow.....Thursday.....will be an interesting day at German banks. They will finally have the 5-Euro coin to issue.
Back in the old days....when we had the Deutsche Marks....there was a 5-DM coin. It was a popular coin and people tended to use it a good bit. Ever since the Euro came along, there's been this desire by the public to have a larger domination coin other than the one or two Euro coin.
Getting one tomorrow? Well....that may be a problem. Most news sources say that here in the initial period, there are only a certain amount of the coins and they expect collectors to be hyped up and get most of the coins for collections, so they won't be in circulation much.
Getting paid back at the store with a coin? I'd take a guess that it might be three or four months before you start to see 5-Euro coins as pay-back.
Value as a collector's item? Maybe in forty years.....it might be worth ten to fifteen Euro as a 2016 coin and in perfect condition. The idea of rushing in and getting a couple is mostly a joke.