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 $239.49   11.326%   $266.6146   $266.61   $266.60   $266.60  
  Purchase #2 $193.37   8.512%   $209.8297   $209.83   $209.85   $209.80  
  Purchase #3 $213.86   4.170%   $222.778   $222.78   $222.80   $222.80  
  Purchase #4 $82.95   12.832%   $93.5941   $93.59   $93.60   $93.60  
  Purchase #5 $69.34   13.285%   $78.5518   $78.55   $78.55   $78.60  
  Purchase #6 $119.96   11.854%   $134.1801   $134.18   $134.20   $134.20  
  Purchase #7 $186.38   13.259%   $211.0921   $211.09   $211.10   $211.10  
  7 purchase totals = $1,105.35       $1,216.6404   $1,216.63   $1,216.70   $1,216.70