miscalculation on "100*e-6"

[cools0607]

I am trying to make a calculation: 100*e-6, but got wrong answer: 9.999999999999999e-05.
I also tried: 100*0.000001
All of them are not reasonable.

100*1e-6
Out[103]: 9.999999999999999e-05

100*0.000001
Out[104]: 9.999999999999999e-05

But 100*1e-5 is correct.

100*1e-5
Out[105]: 0.001