Are you looking for connection design within STAAD or a separate program.
If you're talking about a separate program, then don't worry about the taper. Unless the rate of taper is really severe you can design the connection using the end properties of the beam and you should be fine.
It depends on what types of connections you're looking for, but I would encourage you to at least look at the Demo version of RISAConnection. The interface is so much simpler to use.
Since this is posted in the STAAD forum, it's worth mentioning that Staad.pro with Ram Connection (or Ram Connection stand-alone) is another good option
The latest version of Ram Connection has several good connections for moment end plates using tapered or haunched sections (as well as all the typical stuff).
you made me think : does the section being tapered or not affect the connections ? i mean taper is along the length and the connection design is to done with forces at the connection point and taking into consideration the section value at that very point. how does Taper or no taper affect connection ?
We see the end plate might be detailed in various positions; vertical, horizontal, or perpendicular the tapered beam for example, which also affects orientation of stiffener plates.