In that case the simplest answer is to just use the BEST format and leave it at that. That is recognizable to humans. There is no need to tell a human 1 euro per unit is the same as 1.00 euro per unit.
But there are probably other issues you need to address. What ever method you use to represent a number like 1/3 that cannot be expressed exactly as a binary number will be non-exact. So you need to know how many decimal places will be used by the algorithms that use those numbers. Then just display ALL of the values to that number of decimal places.
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