Problem Calculating Fractions

I routinely accept payments on behalf of a client. For my work, I charge a 33 1/3% commission. I have tried to set this up in a spreadsheet to calculate payment (column A) minus commission (column (column A)) equals profit to client (column C).

I have tried several formulas, all of which render outputs that are not always exactly accurate.

As an example, if I enter 100 in Column A, and formula A/3 in B, the output is correct:
100.00 -33.33 66.67

The output is INCORRECT if 50 is entered in Column A; for my purposes the calculation needs to be exact or 16.67:

50.00 -16.66 33.34

To try to resolve this problem, I used the ROUNDUP function. This fixes the problem with an input of 50 but causes a problem with an input of 100.

Finally, I also tried using the TRUNC function. The TRUNC function gives me similar results; most of the outputs are correct, but some are off by a penny.

I've attached a copy of the most recent spreadsheet that I used.