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 $230.38   13.498%   $261.4767   $261.48   $261.50   $261.50  
  Purchase #2 $16.25   3.134%   $16.7593   $16.76   $16.75   $16.80  
  Purchase #3 $209.46   12.386%   $235.4037   $235.40   $235.40   $235.40  
  Purchase #4 $10.25   6.871%   $10.9543   $10.95   $10.95   $11.00  
  Purchase #5 $200.85   12.338%   $225.6309   $225.63   $225.65   $225.60  
  Purchase #6 $51.87   4.507%   $54.2078   $54.21   $54.20   $54.20  
  Purchase #7 $182.94   5.220%   $192.4895   $192.49   $192.50   $192.50  
  7 purchase totals = $902.00       $996.9222   $996.92   $996.95   $997.00