Depending on the size of your tile, you might be able to get away with just putting a column of cut tiles in the center of the U and a row of cut tiles at the bottom of each leg of the U. Or use something like Schluter edging.

They do make bullnose tiles for edges that have a rounded edge. If the tile that you are using does not have edge pieces that you can get, you could pick an accent tile to border it that has bullnose tiles, use a decorative tile molding (pencil, dental, etc.), caulk the edge, or lightly sand and stain the edge to match the rest of the tile (last resort). We do that with travertine in the showers (not sure exactly how the tile guy does that).

There are also a wide variety of metal edges and trims that fit the bill.