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 $149.42   10.703%   $165.4124   $165.41   $165.40   $165.40  
  Purchase #2 $57.95   8.635%   $62.954   $62.95   $62.95   $63.00  
  Purchase #3 $103.70   11.771%   $115.9065   $115.91   $115.90   $115.90  
  Purchase #4 $202.89   8.861%   $220.8681   $220.87   $220.85   $220.90  
  Purchase #5 $114.43   6.128%   $121.4423   $121.44   $121.45   $121.40  
  Purchase #6 $242.81   5.786%   $256.859   $256.86   $256.85   $256.90  
  Purchase #7 $103.92   12.296%   $116.698   $116.70   $116.70   $116.70  
  7 purchase totals = $975.12       $1,060.1403   $1,060.14   $1,060.10   $1,060.20