Yup, the exploding dice rolling mechanic is a known issue with Roll20 @Carl.
So, crazy news folks! For folks like @Hassurunous, @GartLarissa, @Daranar, you’ll either find this hilarious or hate me
As it turns out, the calculations for most die roll stat charts have been wrong all along 
I’ve been too busy working on other things, my buddy who made http://spandox.com/rollopen.htm is a veteran computer programmer so I never bothered to check his work UNTIL NOW!
I’m laughing maniacally, knowing how it’s not as big of a deal as people will think it is and also bracing myself for a storm of controversy.
Turns out, the the thing that’s wrong on Roll20 was also wrong on http://spandox.com/rollopen.htm this entire time 
I’ve fixed the logic and forked a new (correct) version. The impact on the average (naturally) scales depending on how much advantage you have, and the miscalculation can be quite dramatic at high advantage totals.
Previously - d20 + 3d10 (Advantage 10) = ~45.99
Correct - d20 + 3d10 (Advantage 10) = ~39.13
Previously, getting a 70+ on that roll had a 4.06% chance
Turns out, it’s actually 0.46%
Without further adieu, you can check out the fixed stat generator (I’ll redo the user interface later when I have time) at: