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 $23.94   12.452%   $26.921   $26.92   $26.90   $26.90  
  Purchase #2 $57.73   7.814%   $62.241   $62.24   $62.25   $62.20  
  Purchase #3 $155.42   8.837%   $169.1545   $169.15   $169.15   $169.20  
  Purchase #4 $57.81   5.730%   $61.1225   $61.12   $61.10   $61.10  
  Purchase #5 $123.45   8.517%   $133.9642   $133.96   $133.95   $134.00  
  Purchase #6 $234.66   11.600%   $261.8806   $261.88   $261.90   $261.90  
  Purchase #7 $74.62   4.664%   $78.1003   $78.10   $78.10   $78.10  
  7 purchase totals = $727.63       $793.3841   $793.37   $793.35   $793.40