Hi Hassan,
Some time ago ... I also tried to find a way to modify these main controls.
I have no found reference in the Retail SDK. I believe that these main controls are locked.
I managed to find some reference the properties of these objects "decompiler" the .dll POSProcesses. (TotalAmount and Receipt class in WinControls) however, we can not change these classes.
Alternatively, you can try to change the width / height of the columns/fields in AX Designer
Retail\Setup\POS\Screen Layouts\Designer
Please, if you find otherwise, share with us. Or if you can, open a incident in MS.
Look this post:
https://community.dynamics.com/ax/f/33/t/154742
I Hope this Helps!
Regards,
Rodolfo Recalde.