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 $49.84   7.407%   $53.5316   $53.53   $53.55   $53.50  
  Purchase #2 $228.39   13.577%   $259.3985   $259.40   $259.40   $259.40  
  Purchase #3 $89.49   8.105%   $96.7432   $96.74   $96.75   $96.70  
  Purchase #4 $248.93   4.670%   $260.555   $260.56   $260.55   $260.60  
  Purchase #5 $152.91   5.546%   $161.3904   $161.39   $161.40   $161.40  
  Purchase #6 $21.70   5.755%   $22.9488   $22.95   $22.95   $22.90  
  Purchase #7 $78.90   4.867%   $82.7401   $82.74   $82.75   $82.70  
  7 purchase totals = $870.16       $937.3076   $937.31   $937.35   $937.20