How can I align parts to a certain stud grid?

Alright so I'm trying to make a gui button that when clicked, it inserts a model that is moved to the mouse until the player clicks to place it. Everything works so far, but I'm trying to get it to align to a stud grid of 25 studs so that everything is even. The script:

InsertId = 184711756
Player = script.Parent.Parent.Parent.Parent
Mouse = Player:GetMouse()
local Spawn = game.Workspace.Start
Clicked = false
Placed = false

function Insert()
	if Clicked == true then return end
	Clicked = true
	Placed = false
	local InsertedObject = game:GetService("InsertService"):LoadAsset(InsertId)
	InsertedObject.Parent = Player.PlayerGui
	local Search = InsertedObject:GetChildren()
	for i = 1, #Search do
		Search[i].Parent = game.Workspace.Camera
		InsertedObject:Remove()
		InsertedObject = Search[i]
	end
	InsertedObject.PrimaryPart = InsertedObject.Tile
	local SB = Instance.new("SelectionBox", Player.PlayerGui)
	SB.Color = BrickColor.new("Teal")
	SB.Name = "Place"
	SB.Adornee = InsertedObject.Tile
	while Placed == false do
		wait()
		if (Mouse.Hit.p - Player.Character.Torso.Position).magnitude <= 100 then
			if InsertedObject.Tile.Position.Y == Spawn.Position.Y then
				SB.Color = BrickColor.new("Lime green")
			else
				SB.Color = BrickColor.new("Really red")	
			end
			InsertedObject:MoveTo(Vector3.new(Mouse.Hit.p.X+12.5, Spawn.Position.Y, Mouse.Hit.p.Z+12.5))
		else
			SB.Color = BrickColor.new("Really red")	
		end	
	end
end

function Place()
	if Clicked == false then return	end
	if Placed == true then return end
	if Player.PlayerGui:findFirstChild("Place") then
		if Player.PlayerGui.Place.ClassName == "SelectionBox" then
			if Player.PlayerGui.Place.Color == BrickColor.new("Lime green") then
				Placed = true
				Clicked = false
				local Search = game.Workspace.Camera:GetChildren()
				for i = 1, #Search do
					Search[i].Parent = game.Workspace
				end
				Player.PlayerGui.Place:Remove()
			end
		end
	end
end

Mouse.Button1Down:connect(Place)
script.Parent.MouseButton1Click:connect(Insert)

In order to round any number so it's a factor of a particular value, 25 in your instance, you need to subtract off how far above the number you went. Roblox has a great operation that allows you to find the number you need to subtract. It's called the modulus operation and is represented by a %.

Example: 18%4 = 2 (Because 18/4 = 4 * 4 + 2)

To implement this, we can find the remainder and subtract it from the original number:

InsertedObject:MoveTo(Vector3.new(Mouse.Hit.p.X - Mouse.Hit.p.X%25, Spawn.Position.Y, Mouse.Hit.p.Z - Mouse.Hit.p.Z%25))

This will move it if it based on the centre of the brick, but in your case you want to move it based on the edges. To do this, we simply add half the rounding value to the position.

InsertedObject:MoveTo(Vector3.new((Mouse.Hit.p.X+12.5) - (Mouse.Hit.p.X+12.5)%25, Spawn.Position.Y, (Mouse.Hit.p.Z+12.5) - (Mouse.Hit.p.Z+12.5)%25))

Now just put this in your script, and you should be good to go!