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 $235.46   11.132%   $261.6714   $261.67   $261.65   $261.70  
  Purchase #2 $101.94   12.764%   $114.9516   $114.95   $114.95   $115.00  
  Purchase #3 $229.49   13.177%   $259.7299   $259.73   $259.75   $259.70  
  Purchase #4 $110.27   3.762%   $114.4184   $114.42   $114.40   $114.40  
  Purchase #5 $191.51   3.746%   $198.684   $198.68   $198.70   $198.70  
  Purchase #6 $58.83   5.580%   $62.1127   $62.11   $62.10   $62.10  
  Purchase #7 $115.69   12.588%   $130.2531   $130.25   $130.25   $130.30  
  7 purchase totals = $1,043.19       $1,141.8211   $1,141.81   $1,141.80   $1,141.90