use rtl::math::round here to get the same number on 32/64bit platforms

This fixes sd_import_tests where 100*0.35 was 34 on 32bit platform.

Change-Id: I45705326e91892beb814bd94e074b0a652709768
(cherry picked from commit ba6da9545764f2545313ba085ed4a096165180fd)
Reviewed-on: https://gerrit.libreoffice.org/10385
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>