New track is up called Minecraft-like Pt.1, where you can place about 180 blocks in 4 different colors! They snap to a grid of 1m, and here is how it's done. These should make your blocks' position divisible evenly by the grid size.
Add half of your grid size to center the block to the cursor.

If your grid is simply 1 x 1:
floor(cursor position x,y,z)
This will remove the decimals of your cursor's position.

If your grid is bigger, try:
floor( (cursor position x,y,z) divided by (grid size) ) x grid size

examples
1530.87 / 2 = 765.435
floor(765.435) = 765
765 x 2 = 1530
1530 + (2 / 2) = 1531

1530.87 / 8 = 191.35875
floor(191.35875) = 191
191 x 8 = 1528
1528 + (8 / 2) = 1532

Also check out 'Trials Craft 2' by cpt decoy, who uploaded just before me!