my @rows;
my @this_row;
my $num_per_row = 5;
my $in_this_row = 0;

while ( my $item = $sth->fetchrow_hashref ) {
    push @this_row, $item;
    if ( @this_row >= $num_per_row ) {
        push @rows, [ @this_row ];
        @this_row = ();
    }
}