Yesterday I succeeded in getting my RaspberryPi2B to print on a USB printer (HP LaserJet Pro 400). I then attempted to print results from the Pi version of Mathematica 10. I soon found there is no Print menu in the version I have installed (10.0 for Linux ARM (32 bit) (Feb 3,2015)). However, as a work-around - I found you can Save As (then select PDF) and then print the PDF file that corresponds to the entire notebook with the Pi's PDF Viewer application. Mathematica's Export routine allows finer grained saving of results to PDF.
One way to do this is with
which will bring up the print dialog window.
If you would like to "add" a button to do this, you may create a palette using
CreatePalette[Button["Print me", FrontEndTokenExecute["PrintDialog"]]]
which will create a button that will allow you to print the active notebook.
(truth in advertising - I confirmed this with printing as a PDF; I do not have access to a printer on my RPi)