( Note: I assumed $total_nums contains an integer or that your code was mishandling 30.5 and the like. )

If you invert the order of the checks, you can simplify to the following.

$test_nums = $total_nums > 180 ? $test_nums
           : $total_nums > 150 ? 6
           : $total_nums > 120 ? 5
           : $total_nums >  90 ? 4
           : $total_nums >  60 ? 3
           : $total_nums >  30 ? 2
           :                     1;
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Since the breakpoints form continuous serious of multiples of 30, the above could be simplified further using a loop. Or better yet, using division.

if ( $total_nums <= 0 ) {
   $test_nums = 1;
} elsif ( $total_nums <= 180 ) {
   $test_nums = int( ( $total_nums - 1 ) / 30 ) + 1;
}
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Update: I got sidetracked while writting my reply, so other people have posted similar solutions already. Please excuse any duplication.