I couldn't find a print function for grouped grids, so I made one. This may not be (isn't) the most elegant or efficient way to go about this, but I managed to make it work with Ext 4.0.7 and 4.1.0. I only have done initial testing in Chrome and FF and it suits our needs. I hope someone else finds it useful.

Printer for Grouped grids with or without summary totals.
Will open a new window with the results which can be printed by the browser.
Preserves hidden columns, widths, column order, and collapse status.