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 $126.69   11.854%   $141.7078   $141.71   $141.70   $141.70  
  Purchase #2 $186.32   12.154%   $208.9653   $208.97   $208.95   $209.00  
  Purchase #3 $130.88   7.629%   $140.8648   $140.86   $140.85   $140.90  
  Purchase #4 $231.97   12.800%   $261.6622   $261.66   $261.65   $261.70  
  Purchase #5 $131.85   8.683%   $143.2985   $143.30   $143.30   $143.30  
  Purchase #6 $134.95   11.548%   $150.534   $150.53   $150.55   $150.50  
  Purchase #7 $22.61   11.357%   $25.1778   $25.18   $25.20   $25.20  
  7 purchase totals = $965.27       $1,072.2104   $1,072.21   $1,072.20   $1,072.30