There are 2 variations of this coin. Both are attributed to
Siscia by Estoit.
The first is
not in RIC (first emmission) - there were 18 of these in the LaVenera
hoard.
The second RIC attributed (incorrectly) to
Ticinum. This is
IMP CM CL TACITVS P
AVG - RIC 142, which is from the second emmission of
Siscia. Of this emmission, 10 were found in the LaVenera
hoard.
I would consider both common.
There are a lot of Tactius coins
not in RIC. The best references are
Helvetica's spreadsheets and Estoit. (At least that is what I use). The older versions of RIC (and they are being updated)
had a lot of issues.