ImageSearch Tolerance

[IAMK]

I hacked together a script for work today, and upon execution of _ImageSearch() it turns out the same image was slightly different in different places, so I ended up nesting 5 ifs together...

If($search = 1) Then ;If image is found.
      MouseClick("Primary", $x, $y, 1, 0)
   Else
      $search = _ImageSearch("CheckedBox2.png", 1, $x, $y, 0, 0)

      If($search = 1) Then ;If image is found.
         MouseClick("Primary", $x, $y, 1, 0)
      Else
         $search = _ImageSearch("CheckedBox3.png", 1, $x, $y, 0, 0)

         If($search = 1) Then ;If image is found.
            MouseClick("Primary", $x, $y, 1, 0)
         Else
            $search = _ImageSearch("CheckedBox4.png", 1, $x, $y, 0, 0)

            If($search = 1) Then ;If image is found.
               MouseClick("Primary", $x, $y, 1, 0)
            Else
               $search = _ImageSearch("CheckedBox5.png", 1, $x, $y, 0, 0)

               If($search = 1) Then ;If image is found.
                  MouseClick("Primary", $x, $y, 1, 0)
               EndIf
            EndIf
         EndIf
      EndIf
   EndIf

Looking back on the code now, I could do the entire thing with a tolerance in the last 2 parameters.
However, is there any general guideline on how much tolerance to set? I can't seem to find anything on this topic for AutoIT.