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 $244.26   10.243%   $269.2796   $269.28   $269.30   $269.30  
  Purchase #2 $28.85   6.853%   $30.8271   $30.83   $30.85   $30.80  
  Purchase #3 $30.25   13.149%   $34.2276   $34.23   $34.25   $34.20  
  Purchase #4 $107.85   6.208%   $114.5453   $114.55   $114.55   $114.50  
  Purchase #5 $229.56   8.152%   $248.2737   $248.27   $248.25   $248.30  
  Purchase #6 $224.75   7.701%   $242.058   $242.06   $242.05   $242.10  
  Purchase #7 $16.70   6.477%   $17.7817   $17.78   $17.80   $17.80  
  7 purchase totals = $882.22       $956.9930   $957.00   $957.05   $957.00