So this is not a rare coin then?
Depending on where you are digging/detecting, it is likely relatively uncommon to find a
sestertius compared to the frequency of late
Roman bronze (~
Constantine era onward) - purely based on the extraordinary numbers of late
Roman bronze produced.
It's extremely cool that you found it though. If I was on your
side of the Atlantic I think detecting would be one of my favorite hobbies if I lived in an
area that permitted it. If you are in
Britain (or maybe Croatia?), it might be worthwhile to check the
area for other coins. Those countries have really sensible laws about ancient coin finds that would make looking for them worthwhile.