I doubted the answer I got in the Apple store today when I picked up my 5th generation iPad mini but when I checked against my 2nd generation, they were right.
I have tried the Smart Cover and Leather case for the 2nd generation iPad Mini on my 5th generation and they don’t fit. I picked up a white Smart Cover for my new mini and I’m glad I did. The magnets feel a lot better than the 2nd generation, which although the size is ok it doesn’t stick to the side of the iPad very well.
You can see here it’s not fitting the leather case.
2nd generation Smart Cover is the right size but magnets don’t work.