I've put in a LOT of travertine and tumbled marble on backsplashes. With the inclusions, it is recommended to grout over everything. Yes, this fills the holes....but if your grout is a similar colour as the tile...it looks great, and doesn't collect stains, food bits, bacteria, etc.
"While money can't buy happiness, it certainly lets you choose your own form of misery.”
~ Groucho Marx~
Avanti Tile & Stone