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 $196.72   9.182%   $214.7828   $214.78   $214.80   $214.80  
  Purchase #2 $109.47   4.777%   $114.6994   $114.70   $114.70   $114.70  
  Purchase #3 $133.75   4.266%   $139.4558   $139.46   $139.45   $139.50  
  Purchase #4 $223.42   5.293%   $235.2456   $235.25   $235.25   $235.20  
  Purchase #5 $234.94   11.271%   $261.4201   $261.42   $261.40   $261.40  
  Purchase #6 $50.95   12.461%   $57.2989   $57.30   $57.30   $57.30  
  Purchase #7 $99.28   13.582%   $112.7642   $112.76   $112.75   $112.80  
  7 purchase totals = $1,048.53       $1,135.6668   $1,135.67   $1,135.65   $1,135.70