Looks like S5 may be the last and if not, then S6 should be the finale.
http://www.thewrap.com/boardwalk-emp...ending-series/
This show is about Nucky and S4 pitching Narcisse against Chalky is why I didn't like it all that much. In the Boardwalk universe nobody dies well, they don't get to keep the money and the girl at the end. Essentially, the show is about the rise and fall of many of the characters and the reason I'll come back and watch S5 is to find out how Nucky ends.
Tampa with Sally would be a nice ending for Nucky but that won't be in line with Boardwalk's moral standard. And I don't think death is what the audience are really looking for Nucky so it'll be interesting to find out where the show is going to take us in S5. But I do hope S5 is the end of it.