Keeping travertine clean

We put honed travertine throughout our house when we built it 3 and 1/2 years ago. I hear everyone say they love their travertine so I can only guess we are doing something really wrong because we absolutely hate it. The travertine butts up to each other and where the "grout lines" are, it gets filthy. The only way to keep it looking half way descent is to scrub every line with a scrub brush. We tried sealing half of it to see if that helped with the problem but it didn't. Maybe we used the wrong grout? Not sure. I am at the end of my rope with trying to keep it clean looking. Anything you could tell us would be greatly appreciated....