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 $206.81   4.691%   $216.5115   $216.51   $216.50   $216.50  
  Purchase #2 $239.57   5.874%   $253.6423   $253.64   $253.65   $253.60  
  Purchase #3 $32.82   8.280%   $35.5375   $35.54   $35.55   $35.50  
  Purchase #4 $74.66   4.706%   $78.1735   $78.17   $78.15   $78.20  
  Purchase #5 $249.93   13.639%   $284.018   $284.02   $284.00   $284.00  
  Purchase #6 $135.64   11.813%   $151.6632   $151.66   $151.65   $151.70  
  Purchase #7 $201.69   11.105%   $224.0877   $224.09   $224.10   $224.10  
  7 purchase totals = $1,141.12       $1,243.6337   $1,243.63   $1,243.60   $1,243.60