I think a less ambiguous way of saying what you mean is:

"If there are two bids of the same amount, neither bids can win."

It might help to give an example:

"If we receive bids of 0.1 0.2 0.5 0.1 0.7 0.2 and 1.2 then the bid of 0.5 wins.  0.1 and 0.2 are lower, but both occur multiple times.  0.5 is the lowest *unique* bid".