use POSIX "floor";

my $yearlyamount = 5199.98;
my $weekly1 = sprintf("%.3f", $yearlyamount/52); 
chop($weekly1);
my $weekly2 = floor(100*5199.98/52)/100;       
printf("%5.2f  %5.2f\n", $weekly1, $weekly2);
__END__
100.00  99.99