Again, slant rhyme. Which isn't cheating in a sonnet or a sestina, when you gotta make a bunch of shit fit the scheme, but is totally cheating if it's a single pair.
That, or for a very specific subset of the Southern U.S. (and maybe some other regions, I don't know), those two vowel sounds are in fact the same. Which annoys the living daylights out of me when I encounter it for some reason. I guess it counts as a pet peeve. There are people who do literally pronounce it "re-tell."
Retell - hell?