You can use a regular End Mill (Milling Tool-5 Parameters), and enter a taper angle.
This will only represent the tapered portion of the tool. If you need to display and/or check against the shack, then you can cheat & create a tool holder with the first segment representing the shank of the tool.
OR, you can use a User Defined Tool (MILL_USER_DEFINED), also called a "Form Tool".
User Defined Tools are only used with Planar Profile operations.
"Of course, that's just my opinion. I could be wrong!"
T Briggs (CAM dude) - Siemens PLM Software