1975 D Roosevelt Dime

It is Machine Doubling. Machine Doubling is random on coins. Even from strike to strike it can be different:

Note that all these images are from the same OBW roll and show the same obverse marker. But not the MD is different on each one.
So there will be no listing for machine doubled coins. A list happens on doubled dies and RPM and other variety coins. Machine Doubling is often on normal dies and happens right after the strike, altering the devices like a kick in the shins, damaging the coin. (common) How can I tell that it is Machine Doubling? Look at the devices. Are the devices enlarged or reduced? Is the edges of the devices showing contour on all 4 sides of the devices? On your coin and other MD examples, they are usually showing the contour on 3 sides with the 4 side flat, shelf like where the die swung over and damaged the devices, often in a certain direction. (but not always though)

It is a 'D'. The Machine Doubling altered that SE edge of the mintmark.

The 'P' mintmarks didn't start on coins until 1980 for all denominations except cents. (except for 2017-P)

That is the only year that cents had a 'P' mintmark.

As usual!