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 $240.97   8.536%   $261.5392   $261.54   $261.55   $261.50  
  Purchase #2 $177.72   7.793%   $191.5697   $191.57   $191.55   $191.60  
  Purchase #3 $217.30   12.409%   $244.2648   $244.26   $244.25   $244.30  
  Purchase #4 $176.28   3.633%   $182.6843   $182.68   $182.70   $182.70  
  Purchase #5 $183.45   8.151%   $198.403   $198.40   $198.40   $198.40  
  Purchase #6 $226.50   3.378%   $234.1512   $234.15   $234.15   $234.20  
  Purchase #7 $226.44   5.227%   $238.276   $238.28   $238.30   $238.30  
  7 purchase totals = $1,448.66       $1,550.8882   $1,550.88   $1,550.90   $1,551.00