Unfortunately,
font-variant: small-caps isn't even supported by many ePub readers, but Amazon added
font-variant: small-caps support in KF8.
To ensure that older Kindles will display small caps correctly many ebook producers fake small caps by applying different styles to the first letter and the remaining letters of capitalized text.
Peter Hatch came up with a very
elegant solution, which you can find on his web site
Extraordinary Commons.