Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.27   13.312%   $76.225   $76.23   $76.25   $76.20  
  Purchase #2 $8.75   8.119%   $9.4604   $9.46   $9.45   $9.50  
  Purchase #3 $55.47   7.750%   $59.7689   $59.77   $59.75   $59.80  
  Purchase #4 $24.71   3.630%   $25.607   $25.61   $25.60   $25.60  
  Purchase #5 $123.91   12.652%   $139.5871   $139.59   $139.60   $139.60  
  Purchase #6 $167.39   9.137%   $182.6844   $182.68   $182.70   $182.70  
  Purchase #7 $81.48   6.504%   $86.7795   $86.78   $86.80   $86.80  
  7 purchase totals = $528.98       $580.1123   $580.12   $580.15   $580.20