There is not a built-in way to do it. I requested a similar feature not long ago: Snap to Nth gridline (three requests in one)
You can work around this by building a big grid made up of tiles. Make a new Tile Layer at the top of your layer stack, and make a room-sized rectangle using a solid-coloured tile (or a tile close to solid). Select and copy this rectangle, and paste it diagonal to the first. Now you’ve got the start of a checkerboard pattern. Keep selecting and copy+pasting until you’ve filled your map, and you’ll have a grid for your rooms :D!
You’ll most likely want to set this layer’s opacity very low once you’re done, so you can just barely see it. You’ll also need to remember to hide the layer before you export the map to your game (or ignore this layer explicitly in your import code) so that it doesn’t show up. The grid also won’t automatically update when you add more space to your map, but once you’ve got it going, it’s easy to expand it by copy+pasting large swaths of it.