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 $250.71   4.257%   $261.3827   $261.38   $261.40   $261.40  
  Purchase #2 $179.34   10.403%   $197.9967   $198.00   $198.00   $198.00  
  Purchase #3 $164.62   4.741%   $172.4246   $172.42   $172.40   $172.40  
  Purchase #4 $28.39   8.184%   $30.7134   $30.71   $30.70   $30.70  
  Purchase #5 $126.59   12.688%   $142.6517   $142.65   $142.65   $142.70  
  Purchase #6 $166.77   12.573%   $187.738   $187.74   $187.75   $187.70  
  Purchase #7 $38.34   6.239%   $40.732   $40.73   $40.75   $40.70  
  7 purchase totals = $954.76       $1,033.6391   $1,033.63   $1,033.65   $1,033.60