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 $237.48   10.164%   $261.6175   $261.62   $261.60   $261.60  
  Purchase #2 $130.66   6.133%   $138.6734   $138.67   $138.65   $138.70  
  Purchase #3 $73.40   5.750%   $77.6205   $77.62   $77.60   $77.60  
  Purchase #4 $56.95   3.418%   $58.8966   $58.90   $58.90   $58.90  
  Purchase #5 $42.76   4.618%   $44.7347   $44.73   $44.75   $44.70  
  Purchase #6 $152.89   4.825%   $160.2669   $160.27   $160.25   $160.30  
  Purchase #7 $156.87   3.719%   $162.704   $162.70   $162.70   $162.70  
  7 purchase totals = $851.01       $904.5136   $904.51   $904.45   $904.50