You can use a DFSORT/ICETOOL job like the following to do what you asked for. I assumed your input file has RECFM=FB and LRECL=80, but the job can be changed appropriately for other attributes.
//S1 EXEC PGM=ICETOOL
//TOOLMSG DD SYSOUT=*
//DFSMSG DD SYSOUT=*
//IN DD *
101 10.56
101 10.74
102 34.34
102 45.34
/*
//T1 DD DSN=&&T1,UNIT=SYSDA,SPACE=(CYL,(5,5)),DISP=(,PASS)
//OUT DD SYSOUT=*
//TOOLIN DD *
COPY FROM(IN) USING(CTL1)
SORT FROM(T1) TO(OUT) USING(CTL2)
/*
//CTL1CNTL DD *
INREC OVERLAY=(81:C'1')
OUTFIL FNAMES=T1,REMOVECC,
SECTIONS=(1,3,
TRAILER3=(1,3,5:TOT=(5,5,UFF,EDIT=(IT.TT)),2X,
'Sum for ',1,3,81:C'0'))
/*
//CTL2CNTL DD *
OPTION EQUALS
SORT FIELDS=(1,3,CH,A,81,1,CH,A)
OUTREC BUILD=(1,80)
/*