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 $208.49   7.613%   $224.3623   $224.36   $224.35   $224.40  
  Purchase #2 $125.66   8.379%   $136.1891   $136.19   $136.20   $136.20  
  Purchase #3 $135.55   13.696%   $154.1149   $154.11   $154.10   $154.10  
  Purchase #4 $146.97   5.795%   $155.4869   $155.49   $155.50   $155.50  
  Purchase #5 $53.81   7.203%   $57.6859   $57.69   $57.70   $57.70  
  Purchase #6 $58.99   6.759%   $62.9771   $62.98   $63.00   $63.00  
  Purchase #7 $47.85   5.768%   $50.61   $50.61   $50.60   $50.60  
  7 purchase totals = $777.32       $841.4262   $841.43   $841.45   $841.50