Why does this script keeps makes it rotates to left?

Here's the script:

function rotation(number)
	script.Parent.Rotation = number
	wait(.05)
end

while wait() do
	a = 5
	repeat
	rotation(a)
	a = a - 0.2
	until a == 0
	repeat
		a = a - 0.25
	until a == -5
	repeat
		rotation(a)
		a = a + 0.2
	until a == 0
	repeat
		rotation(a)
		a = a + 0.25
	until a == 5
	a = 5
	rotation(a)
end

Yet everything the title said, so can you help why this script makes the GUI keeps rotates left?

I need to make it become back and forth, but it won't work.

Any help is appreciated.

Hello! So what you are doing with the rotation is not a very good idea, I recommend looking at this article: https://developer.roblox.com/en-us/api-reference/function/GuiObject/TweenPosition