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 $225.61   8.264%   $244.2544   $244.25   $244.25   $244.30  
  Purchase #2 $74.51   5.351%   $78.497   $78.50   $78.50   $78.50  
  Purchase #3 $109.58   3.253%   $113.1446   $113.14   $113.15   $113.10  
  Purchase #4 $228.72   6.340%   $243.2208   $243.22   $243.20   $243.20  
  Purchase #5 $199.66   13.156%   $225.9273   $225.93   $225.95   $225.90  
  Purchase #6 $22.73   3.404%   $23.5037   $23.50   $23.50   $23.50  
  Purchase #7 $35.25   11.774%   $39.4003   $39.40   $39.40   $39.40  
  7 purchase totals = $896.06       $967.9481   $967.94   $967.95   $967.90