This is silly. It's mobile game currency. It's not a big deal. If seeing an odd number day after day bothers you that much then take one day and complete only the GW nodes required to bring it to a multiple of 400.
All other currencies have odd numbers. The shard shop gear items have odd number prices.
Folks can end up with an odd amount any number of ways. The most likely being that you complete your 150th GW to unlock sims and because several times along the way you failed to complete all 12 nodes you're off. And you know what? The player then had a choice. What bothers you more, having 100 currency lingering about or having one more incomplete GW?
Also, this problem goes away at end game. I have over 130k GW currency. An extra 100 or 200 gets lost in the decimal place.
I'd much rather CG focus on something that will have a real effect on the game than this.