Money Script Manager is sorting values wrong?

So there is a glitch that goes like this:

Balance: $100

Buys Item: -$10

Balance: $90

Buys Item: -$50

Balance: $40

Earns $10

Game says + $70

What?

Balance: $110

If that wasn't a good enough explanation here's this. Whenever I buy something, then earn money through some way, I basically gain back all the money I had plus the money I earned so basically I never lose any money, and that's a problem.

Here's the script that I use to change the money values:

local plr = game.Players.LocalPlayer
local cash = plr:WaitForChild("leaderstats"):WaitForChild("Cash")
local previouscash = cash.Value
local addition = script.Parent:WaitForChild("Addition")

local function comma(input)
   local a, b = string.match(input, "(%d+)(%.?%d*)")
   return string.reverse(a):gsub("(%d%d%d)", "%1,"):gsub(",$", ""):reverse() .. (b or "")
end

cash.Changed:connect(function()
--	script.Parent.Sound:Play()
	if tonumber(cash.Value) <= tonumber(previouscash) then
		local difference = previouscash - cash.Value
		addition.Text = ("-" .. comma(difference))
		addition.FontSize = Enum.FontSize.Size48
		previouscash = cash.Value
		wait(0.1)
		addition.FontSize = Enum.FontSize.Size24
		wait(1.9)
		addition.Text = ""
	elseif tonumber(cash.Value) > tonumber(previouscash) then
		local difference = cash.Value - previouscash
		addition.Text = ("+" .. comma(difference))
		addition.FontSize = Enum.FontSize.Size48
		previouscash = cash.Value
		wait(0.1)
		addition.FontSize = Enum.FontSize.Size24
		wait(1.9)
		addition.Text = ""
	end
	
	script.Parent.Text = ("$" .. comma(cash.Value))
end)

while wait() do
	script.Parent.Text = ("$" .. comma(cash.Value))
end