If you are only going up to 180 i don't see why a float is really necessary??? why not just multiply by 100? it'll still get you two digit accuracy
i.e: 180.00 = 18000
as for rounding a floating point number down to four decimals... it is not too hard to do, but why would you need to do it? it's not like reducing the number of decimal points will reduce the processing time more than the cost it takes to round the number.
I think the easiest way to round to four decimals would probably be to mask off the bits of the less significant digits using "&" and a masking variable
(look up bitwise operators)
this may also be of use to u:
http://en.wikipedia.org/wiki/IEEE_754