I start by creating a drum loop or a percussion loop in Acoustica Mixcraft at a specified bpm. I turn into an mp3 file, store it on a usb, connect the usb to my Roland TD-30 Module and play it as a song. I would like to play the drums along with the percussion loop using the internal click, set at the very same bpm. The internal bpm is ALMOST in synch with the tempo of the mp3 file but unfortunately not entirely. At the end of the song you start to hear that they are out of synch. It isn't much, but enough to hear the difference, and hence it will not work. I can adjust the speed of the song (the mp3 file) but only in percentage units and one single percentage unit would be too much. How could this be solved?
I know you wanted to avoid it, but it sounds like any solution may be far more trouble than its worth, so just go with a click on the actual loop.
But if you definitely want it in sync with the internal click I would try these out...
Use a midi out from your drums, set its clock to master. Midi in to your DAW, set clock to external. Set the bpm you want on your drums and then make the tracks using the drums clock as a control
Midi cable from your computer to your drums, headphones into your drums, play the midi sequence in your DAW and you can hear it on your drums. Then export a midi file not a song
Quick and dirty solution: record your MP3 twice, once with a click, once without. Use the version with a click, instead of the drum module's internal click.
More technical solution: synchronise your drum module's tempo with your DAW using MIDI.