Word of these kinds of things tends to get around, even if you don't spread it. In most cases people won't know exactly how much you got to stay, but that won't stop them from assuming you got something, and that something is something they are not getting.

In fact keeping the amount secret can actually make problems worse, by encouraging people to use their imagination to answer the question; then you end up with a situation where you actually got an extra $5K/year, but everyone you work with thinks you got an oil tanker full of Spanish doubloons and a stable full of ponies.