nodejs mocha how to deal with approximate matching

I am using mocha for testing in nodejs.

The problem is I don't know how to deal with matching nth decimal point precision. For example the following code

value.should.equal((0.8+0.4+1/3)/3)

fails with error message

 AssertionError: expected 0.5111111111111111 to equal 0.5111111111111112
      + expected - actual

      -0.5111111111111111
      +0.5111111111111112

But this is the same stuff for me. How to deal with this precision?