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 $130.58   12.263%   $146.593   $146.59   $146.60   $146.60  
  Purchase #2 $124.76   13.625%   $141.7586   $141.76   $141.75   $141.80  
  Purchase #3 $17.51   12.246%   $19.6543   $19.65   $19.65   $19.70  
  Purchase #4 $165.40   6.874%   $176.7696   $176.77   $176.75   $176.80  
  Purchase #5 $90.79   10.195%   $100.046   $100.05   $100.05   $100.00  
  Purchase #6 $15.54   11.686%   $17.356   $17.36   $17.35   $17.40  
  Purchase #7 $249.97   4.735%   $261.8061   $261.81   $261.80   $261.80  
  7 purchase totals = $794.55       $863.9836   $863.99   $863.95   $864.10