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 $89.63   5.296%   $94.3768   $94.38   $94.40   $94.40  
  Purchase #2 $24.35   8.422%   $26.4008   $26.40   $26.40   $26.40  
  Purchase #3 $109.54   12.290%   $123.0025   $123.00   $123.00   $123.00  
  Purchase #4 $230.74   13.358%   $261.5622   $261.56   $261.55   $261.60  
  Purchase #5 $242.62   10.591%   $268.3159   $268.32   $268.30   $268.30  
  Purchase #6 $74.48   5.395%   $78.4982   $78.50   $78.50   $78.50  
  Purchase #7 $145.90   10.621%   $161.396   $161.40   $161.40   $161.40  
  7 purchase totals = $917.26       $1,013.5524   $1,013.56   $1,013.55   $1,013.60