there are two nodes that i know of that will do that for you or you could make a script that does the math, of course im basing this grid on world coordinates and not on a actual grid mesh. the first node is snap to grid float which is built into the engine. it function pretty much by rounding a float to the grid size, so given a grid size of 10, 6 would become 10, 3 would become 0, and 22 would become 20. the second node is grid snap which is part of the victory plugin by Rama. it takes in a vector and does the same thing as the last node but to each axis in this case.
