Candidate example:

    with localcontext() as ctx:
        ctx.prec += 10        # Perform a higher precision calculation
        ctx.rounding = ROUND_05UP # Avoid double rounding of the final calculation step
        s = calculate_something()
    s = +s  # Round the final result back to the default precision

Thoughts:

* This would highlight the intended purpose of ROUND_05UP.
* Usually, it would slightly improve accuracy.
* OTOH, it would rarely make a difference in practice.

https://docs.python.org/3/library/decimal.html#decimal.localcontext

I’m concerned though that the intermediate calculations might be worse off than with some other rounding mode.

Not a good idea in general - this rounding mode is _mostly_ "to zero", and isn't intended for chains of operations. I don't believe I've ever seen it used in a real program, so the current "no example at all" is a fair representation of real usage ;-)

I'll add that the rounding mode is intended to ease emulating fixed-point arithmetic. The decimal spec claimed that was a goal, but there really isn't any direct support for saying, e.g., "I want two digits after the decimal point". Only for specifying total precision, independent of the radix point's position.

So, e.g., if you want to work with tax rates, etc, but keeping results to penny precision,

1. Set the rounding mode to ROUND_05UP with "plenty of" precision digits.

2. To add, say, a statutory 3.578% tax rate to an item with cost C:

       C *= decimal.Decimal("1.03578")
       C = C.quantize(decimal.Decimal(".01"), decimal.ROUND_HALF_UP)

or whatever final rounding mode local statutes require.

I"m not sure anyone other than Mike Cowlishaw realizes that, though ;-)