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 $148.83   10.633%   $164.6551   $164.66   $164.65   $164.70  
  Purchase #2 $248.89   5.137%   $261.6755   $261.68   $261.70   $261.70  
  Purchase #3 $214.76   4.397%   $224.203   $224.20   $224.20   $224.20  
  Purchase #4 $71.41   12.615%   $80.4184   $80.42   $80.40   $80.40  
  Purchase #5 $98.57   13.654%   $112.0287   $112.03   $112.05   $112.00  
  Purchase #6 $21.37   8.158%   $23.1134   $23.11   $23.10   $23.10  
  Purchase #7 $143.60   8.555%   $155.885   $155.89   $155.90   $155.90  
  7 purchase totals = $947.43       $1,021.9791   $1,021.99   $1,022.00   $1,022.00