Scroll backup to the top of the list to see the largest users. What you are showing is somewhere near the bottom. (I can surmise that since this very page uses 144 MB.)
Aside from that, as far as 5 GB being used, is not all that uncommon, especially in these days of memory hogging websites (I have seen some consume up to 1.5GB). Also, if you have any menu apps, cloud storage apps, etc. that run in the background, while they may not be big by themselves, if you have enough of them, they will add up.
In terms of the cache, macOS will keep some previous apps and data in memory to allow for quicker opening. This is however considered "disposable" memory since when more memory is needed, the system will start removing those cached items in favor of new memory requirements.
So basically, don't try to micromanage the memory use and let macOS do its thing. The only time to be concerned is if you get a system notification that there is not enough memory to say open an app or an app has used too much memory.