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 $133.46   10.545%   $147.5334   $147.53   $147.55   $147.50  
  Purchase #2 $167.73   3.838%   $174.1675   $174.17   $174.15   $174.20  
  Purchase #3 $14.29   6.686%   $15.2454   $15.25   $15.25   $15.20  
  Purchase #4 $85.95   8.847%   $93.554   $93.55   $93.55   $93.60  
  Purchase #5 $242.68   12.599%   $273.2553   $273.26   $273.25   $273.30  
  Purchase #6 $43.81   3.225%   $45.2229   $45.22   $45.20   $45.20  
  Purchase #7 $247.45   6.106%   $262.5593   $262.56   $262.55   $262.60  
  7 purchase totals = $935.37       $1,011.5378   $1,011.54   $1,011.50   $1,011.60