I use [[1d100!>96cf<5+?{bonus} ]] . This will explode the d100 at 96 and higher (the !>96 part) and will color the 1-5 red (that's the cf<5 part) so you know that you will need to do another roll to subtract from it. This does have an unfortunate side effect that if you roll a OEup and then a 1-5, it will still show you a red highlight even though the full roll is above 5 but you can mouse-over the result to verify it and can discount those situations. You can use [[ ?{original roll} - 1d100!>96]] to have a macro to
calculate the open ended down roll, but you would have to enter your
original roll when prompted. Unfortunately there is no way to do the open ended downward roll correctly automatically (and you can only do an open ended one direction at at time). If you also need to highlight natural 66 and natural 100 use [[1d100!>96cf<5cf=66cs=66cs=100 +?{bonus} ]] This will color the natural 100 green and the 66 blue in addition to the red for 1-5.