Is this worth grading?

If you look it is mint error S over D maybe hard to see but it's interesting to me.

Welcome to Numista. 

In a word no, the costs of grading are far beyond it's value. There  is no such coin as a 1943 D/S or S/D steel cent variety. This is a 1943S wartime steel cent due to the fact they needed copper for the war effort and temprarily made them out of steel. It looks like a clear S to me. It can only be a D or S but regardless, the values even in uncirculated condition are a modest $3 -$4 respectively. This example I estimate to be in Very Fine condition at best and an estmated value for it would be about .50 - .75 cents at best. 

There is a RPM 1943 S but I suspect what you have is a filled D.  

S -  S/RPM -  D-  Op's example.

I was wrong. The mint mark could not be a filled die but possible a damaged D in the die.

Just pointing out the noticable slant and nibs on the top and bottom of the S like the Op's example while the D is dead flat on the bottom and both nibs of the D are to the left. This is why I concluded it to be an S to my eye. Regardless, this coin is very ordinary and certainly not worth the expense of grading.