Yep, it's a bug. The rounding function is supposed to be using the "round to nearest" value to determine precision (how many digits after the decimal point), but it is instead using the value itself. In the case of the 4th place prize, the actual prize value is $10.40, which, due to conversion, is 10.4. So it's using a precision of 1 (only 1 place after the decimal point). It correctly calculates the rounded down value as $10.25, but drops the 5 so the value has a precision of 1 (10.2). Displayed as currency it becomes $10.20.

Thanks for reporting this. I'll get it fixed for the next beta.