Which numeric keypad layout (PC or register) should be used for a touch panel?

We lately had a usability test for a self-service payment machine. It’s very similar to the e-banking process.

The whole banking process is over a touchscreen until they enter the debit car. The system then switches to the card terminal. The keyboard for entering an account number during the accounting process on the touchscreen is the same layout as PC keyboards have -->3x3 starting with 789 on top and 0 separated in the middle of the 4th row. The keyboard used by the card terminal is the same as for registers or telephones --> 3x3 starting with 123 on top and 0 separated in the middle of the 4th row.

During the test only one user mentioned that the layout is different. But I’m now curious why those things have different layouts and if we should switch the layout for the touchscreen input to the same as the card terminal. That would give some consistency. On the other hand a PC number pad is more consistent with the usually known input during e-banking.

We only can change the touchscreen UI.

Thanks guys and sorry for my bad English, I’m not a native speaker.