How do you make an object follow your mouse on a grid?

I'm trying to get a part to follow my mouse on a grid, but it just feels... off... It does not feel like I'm doing the grid part correctly. I tried using both math.ceil and math.floor;

local camera = workspace.CurrentCamera;
local mouse = game.Players.LocalPlayer:GetMouse();

local previewItem = Instance.new("Part");
previewItem.Parent = game.Workspace;
previewItem.Size = Vector3.new(1, 1, 1);

mouse.Move:Connect(function()
	local unitRay = camera:ScreenPointToRay(mouse.X, mouse.Y);
	local ray = Ray.new(unitRay.Origin, unitRay.Direction * 500);
	
	local part, pos = workspace:FindPartOnRayWithIgnoreList(ray, {game.Players.LocalPlayer.Character, previewItem});
	
	if part then
		previewItem.Position = Vector3.new(math.floor(pos.X / 5) * 5, math.floor(pos.Y / 5) * 5, math.floor(pos.Z / 5) * 5);
	end;
end);

What am I doing wrong and how should I be doing it?

It follows my mouse perfectly without the grid code, the grid code is causing the issue.