Possessive s: Having it both ways

[P2052 at AOL.COM]

I thought that pronunciation determined whether or not the 's is added to a
name already ending in -s.  For example, if one pronounces the possessive
form of Jesus as Je-sus, then only the apostrophe is used (Jesus').  However,
if one pronounces it as Je-sus-es, then one uses the 's (Jesus's).   I don't
remember where I heard (or read) this, but it seemed plausible, so I
internalized it.  If it's not, please advise.
                           PAT