Small Basic - Mystery of Round Operation

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Computer calculation always has some errors.  I wrote following program to investigate how Math.Round operation works.  Guess what type of errors occur in following case.

TextWindow.WriteLine(Math.Round("2.50000000000000017763568394"))    ' 2

TextWindow.WriteLine(Math.Round( 2.5000000000000001776356839401 ))  ' 2

TextWindow.WriteLine(Math.Round("2.500000000000000200000"))         ' 2

TextWindow.WriteLine(Math.Round("2.5000000000000002000"))           ' 2

TextWindow.WriteLine(Math.Round("2.500000000000000200"))            ' 2

TextWindow.WriteLine(Math.Round("2.5000000000000002"))              ' 2

TextWindow.WriteLine(Math.Round( 2.5000000000000051 ))              ' 2

TextWindow.WriteLine(Math.Round( 2.5000000000000052 ))              ' 3

TextWindow.WriteLine(Math.Round("2.5000000000000001776356839401"))  ' 3

TextWindow.WriteLine(Math.Round("2.50000000000000020"))             ' 3

Actuary, I can't understand yet what happens in the program above...