Okay, it’s kinda late for this but, well, better late than never.
There’s no ‘automatic’ letter grade process and, frankly, you don’t want one. You need to be able to manually adjust for students who are ‘on the bubble’ or to nudge grades up for a student who has worked hard but missed the next letter grade by less than 1 point.
And, no, there’s no way to manage the number of decimal places. Believe me, we’ve looked. The default is 2 decimal places and if you have a fractional grade, it will automatically go out to 5 (!) decimal places. And you cannot control that.
In your Full Grade Center, select Create Column.
Give the column an intelligent name (i.e. one students will understand! 😉 ).
The important step.
Make the Primary Display “text” and enter a number in the Possible Points. (Clickee the pic to embiggen.)
You need “Text” and not “Letter” because the Letter option doesn’t understand about IP grades. And the Points Possible value should, but does not have to, represent the total points in your course. Honestly, you just need a number in the field and 100 is as benign as anything.
Scroll down and turn off the “Include this Column in Grade Center Calculations.”
You don’t want to confuse your grading with anything else!
Click Submit and now you have someplace to put your final letter grade and students can see it in their gradebook!