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 $219.97   7.410%   $236.2698   $236.27   $236.25   $236.30  
  Purchase #2 $125.69   10.315%   $138.6549   $138.65   $138.65   $138.70  
  Purchase #3 $77.80   8.159%   $84.1477   $84.15   $84.15   $84.10  
  Purchase #4 $218.95   11.179%   $243.4264   $243.43   $243.45   $243.40  
  Purchase #5 $144.62   11.105%   $160.6801   $160.68   $160.70   $160.70  
  Purchase #6 $26.27   8.437%   $28.4864   $28.49   $28.50   $28.50  
  Purchase #7 $146.66   13.271%   $166.1232   $166.12   $166.10   $166.10  
  7 purchase totals = $959.96       $1,057.7885   $1,057.79   $1,057.80   $1,057.80