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 $232.89   6.684%   $248.4564   $248.46   $248.45   $248.50  
  Purchase #2 $65.75   8.358%   $71.2454   $71.25   $71.25   $71.20  
  Purchase #3 $231.44   10.692%   $256.1856   $256.19   $256.20   $256.20  
  Purchase #4 $246.39   7.870%   $265.7809   $265.78   $265.80   $265.80  
  Purchase #5 $52.62   5.791%   $55.6672   $55.67   $55.65   $55.70  
  Purchase #6 $188.49   10.779%   $208.8073   $208.81   $208.80   $208.80  
  Purchase #7 $54.78   4.172%   $57.0654   $57.07   $57.05   $57.10  
  7 purchase totals = $1,072.36       $1,163.2082   $1,163.23   $1,163.20   $1,163.30