Perl will use the floating point library for the C compiler used to build it, so I would expect (but not guarantee) that a C interface to the database would give the same answer as the perl interface.
Double precision only has 15 or 16 significant digits, so the "4" in the right-most place is almost certainly not significant. See, for example,http://www.monash.edu.au/policy/gpnumacc.htm#SignificantFigures.
Information about American English usage here and here. Floating point issues? Please read this before posting. — emc