scientific notation - truncation



Hi,

sorry I looked into the manual but I cannot find a solution:

(%i74) 0.0017;
(%o74)            0.0017
(%i75) 0.00017;
(%o75)       1.7000000000000001E-4

why is the second example displayed like that? I guess it has something 
to do with the floating point precision, but i would like to prevent it, 
I don't care about any loss of precision.
I mean, I'd like that 0.00017 results either in 0.00017 (exactly the 
same) or 1.7E-4

Thank you very much

MF