My Code Wont Make The Block Snap To Grid While Generating Terrain?

local X = 50
local Z = 50
local Y = 1

local grid = {}

for x = 1, X do
	grid[x] = {}
	for y = 1, Y do
		grid[x][y] = {}
		for z = 1, Z do
			grid[x][y][z] = math.noise(x/10, z/10) * 15
		end
	end
end

for x = 1, X do
	for z = 1, Z do
		for y = 1,Y do
			local yPos = grid[x][y][z]
			local part = Instance.new("Part")
			part.Anchored = true
			part.Material = Enum.Material.Grass
			part.BrickColor = BrickColor.new("Earth green")
			part.Position = Vector3.new(x*3, yPos, z*3) -- Makes The Block Not Snap To Grid The yPos Is The Problem I Think
			part.Size = Vector3.new(3, 3, 3)
			part.Parent = workspace.TerrainFolder
		end
	end
end

Answered

local X = 30
local Z = 30
local Y = 5

local function STG(X)
	return math.floor(X / 3 + 0.5) * 3
end

local grid = {}

for x = 1, X do
	grid[x] = {}
	for y = 1, Y do
		grid[x][y] = {}
		for z = 1, Z do
			grid[x][y][z] = math.noise(x/10 ,y/10,z/10) * 15
		end
	end
end

for x = 1, X do
	for z = 1, Z do
		for y = 1,Y do
			local yPos = grid[x][y][z]
			local part = Instance.new("Part")
			part.Anchored = true
			part.Material = Enum.Material.Grass
			part.BrickColor = BrickColor.new("Earth green")
			part.Position = Vector3.new(x*3, STG(yPos), z*3) 
			part.Size = Vector3.new(3, 3, 3)
			part.Parent = workspace.Twerrain
		end
	end
end