I'm not sure that rounding would explain that. It may explain 5.01 down to 5.00, but not down to 4.99. I suspect it is because Strava often ignore the distances in the file and recalculate the distances themselves. By default the app uses Apple's distances, which are pedometer based, whereas Strava sometimes recalculate using the GPS locations in the file.
To be honest a 0.4% difference is not bad when transferring workouts between systems which may use completely different ways to calculate distance, although I realise that it makes a big difference because it goes from over 5k to under 5k.
How are you sending the workout to Strava, and if it is direct from WorkOutDoors then what file type are you using? The app uses FIT by default, but you may have changed it in the Export Options screen of the Settings tab. If so then change it back to use FIT. If you are using GPX then that does not contain distances, so it forces Strava to recalculate them, but if you use FIT then you are at least sending the distances, so Strava usually respects them. But not always.