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 $95.63   6.444%   $101.7924   $101.79   $101.80   $101.80  
  Purchase #2 $236.53   8.554%   $256.7628   $256.76   $256.75   $256.80  
  Purchase #3 $44.58   12.688%   $50.2363   $50.24   $50.25   $50.20  
  Purchase #4 $54.65   8.337%   $59.2062   $59.21   $59.20   $59.20  
  Purchase #5 $97.58   5.241%   $102.6942   $102.69   $102.70   $102.70  
  Purchase #6 $121.64   8.149%   $131.5524   $131.55   $131.55   $131.60  
  Purchase #7 $247.60   5.705%   $261.7256   $261.73   $261.75   $261.70  
  7 purchase totals = $898.21       $963.9699   $963.97   $964.00   $964.00