1/2 of a whole not calculating

1/2 quantities are not calculating correctly on 0.5 amounts BUT they are calculating correctly on any half numbers higher than 1 ( ie 1.5, 2.5, 3.5)

For example on https://meadowview.cc/product/achillea-m-sunny-seduction-pp-20808/ if you enter .5 quantities it is $0.54, 1 comes to $54, and 1.5 comes to $81. The .5 quantity is not correct but the others are.

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