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 $226.45   10.668%   $250.6077   $250.61   $250.60   $250.60  
  Purchase #2 $119.95   5.655%   $126.7332   $126.73   $126.75   $126.70  
  Purchase #3 $236.87   9.803%   $260.0904   $260.09   $260.10   $260.10  
  Purchase #4 $68.38   9.338%   $74.7653   $74.77   $74.75   $74.80  
  Purchase #5 $44.59   13.847%   $50.7644   $50.76   $50.75   $50.80  
  Purchase #6 $132.26   5.208%   $139.1481   $139.15   $139.15   $139.10  
  Purchase #7 $32.47   6.863%   $34.6984   $34.70   $34.70   $34.70  
  7 purchase totals = $860.97       $936.8075   $936.81   $936.80   $936.80