OK, after reading that article (thank you Paul) and many others, I added modified every calculation I was using that involved a decimal value (.18 for tax, .07 for surcharge and .015-.035 fro discount) to the following tResults.
Code:double tResult = 0; tResult = totalFCost * TIP_TAX_RATE; // .18 return floor((tResult + 0.005) * 100) / 100;