If you download the rom zip files from a tv box there's a chance that it will come to you in a .bin format. The solution is to go into your file explorer or file manager on your box and simply change the file extension back to .zip. After you do that you will be able to open the zip file as normal. If you download from a PC you will not have this issue.
The Sega Genesis and Master System use the same emulator
Sega Genesis emulator
100 game zip folder
114 Sega Master System Roms