Unexpected output precision and/or rounding results in IronPython 3.4.0

Description

print - whether in conjunction with round or not - does not yield the expected output of decimal values as in 2.7

Steps to Reproduce

While I first observed the behavior in some breaking Unit tests while porting my .NET application to IronPython 3.4.0 using the new nupkg, a simple console example should do:

IronPython 3.4.0 (3.4.0.1000)
[.NETFramework,Version=v4.6.2 on .NET Framework 4.8.4515.0 (64-bit)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print(685.86)
685.86000000000001
>>> f = float(685.86)
>>> print(f)
685.86000000000001
>>> print(round(f,2))
685.86000000000001
>>> print(round(f))
686
>>> print(round(f,1))
685.89999999999998
>>>

Therefore, I'd think of an output rather than a numeric issue.

Expected behavior:
While I am aware that not every decimal number can be rendered in full fidelity, I would expect the same output as was the input argument; or in case of round the output being truncated to the specified number of decimal places. This was the case in IronPython 2.7.

Actual behavior:
Although the result may be correct from a numeric point of view, the numbers always seem to be output with the same number of decimal places, which is never the one provided as an argument. Especially, rounding to 1 digit should not give me 14 digits.

Versions

• 3.4.0 Release

If this is indeed expected, then I am not sure how to produce a normalized output.

Start with the provided IronPython 3.4.0 console reproduction for print(), float(), and round() using 685.86, then compare those results with IronPython 2.7 behavior. Trace the float formatting and rounding entry points to determine whether the discrepancy is in numeric conversion or output formatting; done means the reproduced values have the expected decimal rendering without changing numeric correctness.