100

Start the sequence with non zero digits so that the result of desired arithmetic operation is zero.

12+3-4+5+67+8+9=100

123+4-5+67-89=100
other cases

1=148 / 296 + 35/70

100 = 33 X 3 +3/3


1+2+34-5+67+89-8+9=100

12+3-4+5+67+8+9=100

123-4-5-6-7+8-9=100

1+2.3-4+5+6.7+89=100
and many more