Maybe I didn't look close enough, but I couldn't figure out how to make a blanket rule (for example, increment of 10) for every single category without checking every single (100+) category. Which for me didn't work so well.
[ignore]Also, there's a way of doing this plugin via a functions.php update, per WooCommerce:
So I ended up doing that, since I only needed to adjust my quantity increments and already purchased Woo's min/max plugin.[/ignore]
ETA: OK, so after lots of playing around, I ended up using this plugin despite my boasting above lol. The functions.php version didn't work once in the shopping cart, so it was useless. This plugin though does, which is amazing. THANK YOU! :)