You could avoid doing math all together and treat the problem as a string manipulation exercise:

#! perl -slw
use strict;

while( <DATA> ) {
    chomp;
    printf "Before '%s' becomes ", $_;
    s[ ( \d+ )+ (?: \. ( \d{0,2} ) ( \d* ) )? % ]{
        local $^W;
        my $n = substr( $2 . '00', 0, 2 );
        ($1||'') . $n . ( length($3) ? ".$3" : '' );
    }xe;
    print "'$_'";
}

__DATA__
0.781063003540039%
2.25%
1.455%
4.9%
0.79%
75%
1.15%
0.45999999999999996%
0.9199999999999999%
0.22999999999999998%
1.3%
[download]

Gives:

c:\test>junk4
Before '0.781063003540039%' becomes '78.1063003540039'
Before '2.25%' becomes '225'
Before '1.455%' becomes '145.5'
Before '4.9%' becomes '490'
Before '0.79%' becomes '79'
Before '75%' becomes '7500'
Before '1.15%' becomes '115'
Before '0.45999999999999996%' becomes '45.999999999999996'
Before '0.9199999999999999%' becomes '91.99999999999999'
Before '0.22999999999999998%' becomes '22.999999999999998'
Before '1.3%' becomes '130'
[download]