my %num = (15=>1, 20=>2, 25=>3, 30=>4);

print $_, ' maps to ', $num{ ( 1 + int( ($_ - 1) / 5) ) * 5}, $/ for 10 .. 31
10  maps to  Use of uninitialized value in print 
11  maps to  1
12  maps to  1
13  maps to  1
14  maps to  1
15  maps to  1
16  maps to  2
17  maps to  2
18  maps to  2
19  maps to  2
20  maps to  2
21  maps to  3
22  maps to  3
23  maps to  3
24  maps to  3
25  maps to  3
26  maps to  4
27  maps to  4
28  maps to  4
29  maps to  4
30  maps to  4
31  maps to  Use of uninitialized value in print 

##</code><code>##

for my $num (10,15,16,22,27,30,31) { 
    print $num, $num{
        ( 
            grep{ $_ >= $num } 
            sort{ $a <=> $b } keys %num 
        )[0]}, 
        $/; 
}