old3eyes: Why not just top up $20  and every 5th month you won't have to top up.  Geez there's not much difference between $16 and $20 these days..

It may be partially OCD, but I like to keep my balance always at zero so I can't accidentally pay for anything. 

If you have your card saved you can do $16 by the *888# menu, I think it was just something that got overlooked by the people who designed the new site, as they were not from skinny, probably didnt realise that you were meant to be able to topup exact amounts. Im sure it will get fixed