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 $105.76   8.523%   $114.7739   $114.77   $114.75   $114.80  
  Purchase #2 $72.42   7.259%   $77.677   $77.68   $77.70   $77.70  
  Purchase #3 $42.90   3.619%   $44.4526   $44.45   $44.45   $44.50  
  Purchase #4 $229.97   8.606%   $249.7612   $249.76   $249.75   $249.80  
  Purchase #5 $55.48   12.461%   $62.3934   $62.39   $62.40   $62.40  
  Purchase #6 $220.54   13.420%   $250.1365   $250.14   $250.15   $250.10  
  Purchase #7 $188.36   5.109%   $197.9833   $197.98   $198.00   $198.00  
  7 purchase totals = $915.43       $997.1779   $997.17   $997.20   $997.30