If its about CV, you can mention anything you want.
However, If you are filling the application then mention the designation you are given. If you are promoted, then you can mention the promoted title.
Is inflation in job title in CV considered usual?
At my first job, my title was "engineer". "senior engineer" were much senior for the entry-level person to have that title.
Can people share their opinions... I've not seen much of this in high technology world.