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 $64.42   6.183%   $68.4031   $68.40   $68.40   $68.40  
  Purchase #2 $242.57   6.290%   $257.8277   $257.83   $257.85   $257.80  
  Purchase #3 $48.89   5.768%   $51.71   $51.71   $51.70   $51.70  
  Purchase #4 $140.87   6.102%   $149.4659   $149.47   $149.45   $149.50  
  Purchase #5 $15.38   8.417%   $16.6745   $16.67   $16.65   $16.70  
  Purchase #6 $152.66   3.258%   $157.6337   $157.63   $157.65   $157.60  
  Purchase #7 $89.95   13.788%   $102.3523   $102.35   $102.35   $102.40  
  7 purchase totals = $754.74       $804.0672   $804.06   $804.05   $804.10