In detail rows, PROC REPORT displays the value of Sales with the format specified in its definition (COMMA10.2). The compute block specifies an alternate format to use in the current column on summary rows. Summary rows are identified as a value other than a blank for _BREAK_. 
   compute sales;
      if _break_ ne ' ' then
      call define(_col_,"format","dollar11.2");
   endcomp;