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 $160.41   9.694%   $175.9601   $175.96   $175.95   $176.00  
  Purchase #2 $113.47   11.684%   $126.7278   $126.73   $126.75   $126.70  
  Purchase #3 $140.36   4.628%   $146.8559   $146.86   $146.85   $146.90  
  Purchase #4 $150.48   5.632%   $158.955   $158.96   $158.95   $159.00  
  Purchase #5 $51.63   6.403%   $54.9359   $54.94   $54.95   $54.90  
  Purchase #6 $9.30   10.345%   $10.2621   $10.26   $10.25   $10.30  
  Purchase #7 $232.58   12.645%   $261.9897   $261.99   $262.00   $262.00  
  7 purchase totals = $858.23       $935.6865   $935.70   $935.70   $935.80