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 $208.53   12.662%   $234.9341   $234.93   $234.95   $234.90  
  Purchase #2 $130.46   12.420%   $146.6631   $146.66   $146.65   $146.70  
  Purchase #3 $55.54   11.761%   $62.0721   $62.07   $62.05   $62.10  
  Purchase #4 $229.91   13.821%   $261.6859   $261.69   $261.70   $261.70  
  Purchase #5 $136.95   4.669%   $143.3442   $143.34   $143.35   $143.30  
  Purchase #6 $219.47   11.688%   $245.1217   $245.12   $245.10   $245.10  
  Purchase #7 $47.91   11.574%   $53.4551   $53.46   $53.45   $53.50  
  7 purchase totals = $1,028.77       $1,147.2762   $1,147.27   $1,147.25   $1,147.30