This poem was a bit unusual in the way it came about.  It's one of the few that wasn't directly suggested by someone.  I had been working on the suggestion "sewer" and came up with the rhyme of "fewer" and the idea of substituting the word "less" where "fewer" was expected.  

But there wasn't enough room in the original poem to build a context where it made sense.  So "fewer" budded off into its own poem, and the idea flip-flopped a couple times as to whether "fewer" should be the expected rhyme and "less" would be the actual word, or vice versa.  Eventually I decided that the more pedantic way was funnier.

I've a sin that I have to confess.
When I go to the store, I transgress.
I take 12 jugs of wine
Through the line with the sign
That says, “Only 10 items or fewer.”

Based on the suggestion: “fewer”