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 $231.48   10.723%   $256.3016   $256.30   $256.30   $256.30  
  Purchase #2 $151.49   11.775%   $169.3279   $169.33   $169.35   $169.30  
  Purchase #3 $114.26   11.507%   $127.4079   $127.41   $127.40   $127.40  
  Purchase #4 $171.39   8.659%   $186.2307   $186.23   $186.25   $186.20  
  Purchase #5 $242.71   9.296%   $265.2723   $265.27   $265.25   $265.30  
  Purchase #6 $68.89   8.418%   $74.6892   $74.69   $74.70   $74.70  
  Purchase #7 $112.85   5.614%   $119.1854   $119.19   $119.20   $119.20  
  7 purchase totals = $1,093.07       $1,198.4150   $1,198.42   $1,198.45   $1,198.40