It makes no difference performance-wise, if it did, there’d be something seriously wrong with WordPress.
The same goes for Google, if a lot of super smart people earning 100k salaries can’t write software that handles a trailing slash, then something is terribly wrong with the world.
Either way, WordPress puts the rel="canonical" tag in the header so regardless of wether there’s a trailing slash or not when you visit the page, Google will see that tag and see what the canonical authoritative URL for that page is.
As a side-note, Google doesn’t reserve special rules for WordPress sites, they’re all just sites as far as Google is concerned.