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 $112.44   10.750%   $124.5273   $124.53   $124.55   $124.50  
  Purchase #2 $195.89   9.724%   $214.9383   $214.94   $214.95   $214.90  
  Purchase #3 $59.49   4.583%   $62.2164   $62.22   $62.20   $62.20  
  Purchase #4 $177.36   13.317%   $200.979   $200.98   $201.00   $201.00  
  Purchase #5 $111.49   7.262%   $119.5864   $119.59   $119.60   $119.60  
  Purchase #6 $96.44   4.555%   $100.8328   $100.83   $100.85   $100.80  
  Purchase #7 $228.63   9.271%   $249.8263   $249.83   $249.85   $249.80  
  7 purchase totals = $981.74       $1,072.9065   $1,072.92   $1,073.00   $1,072.80