I don't play banjo (I have a tenor sitting in the closet waiting for me to refurbish it) but I use Tabledit for guitar tabs. I know it also does banjo tabs and I believe its authors claim it handles the fifth string correctly. It's shareware ($55 US registration) and the demo version can be found at:
Click here
Here's another link which has some software suggestions (you'll need to scroll down the page a bit for the tab software):
Click here