I also found some PDB file format. It looks like every manufactor have his own file format for their devices?

I'm sure that they look the way they do because older ones, at least, only supported bitmap fonts. That would suggest that it's not TTF or OTF. That said, there may be modern cash registers that are more powerful.

You could probably call a cash register company if you don't get an answer here.

Thanks Thomas, I'll do. That's the safest way.

It seems, like with same applications for different brands of mobile phones, that every manufactor do things on his own way.