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 $112.31   11.215%   $124.9056   $124.91   $124.90   $124.90  
  Purchase #2 $249.72   7.271%   $267.8771   $267.88   $267.90   $267.90  
  Purchase #3 $119.30   9.135%   $130.1981   $130.20   $130.20   $130.20  
  Purchase #4 $27.86   9.863%   $30.6078   $30.61   $30.60   $30.60  
  Purchase #5 $78.99   4.300%   $82.3866   $82.39   $82.40   $82.40  
  Purchase #6 $174.53   11.724%   $194.9919   $194.99   $195.00   $195.00  
  Purchase #7 $188.34   7.500%   $202.4655   $202.47   $202.45   $202.50  
  7 purchase totals = $951.05       $1,033.4326   $1,033.45   $1,033.45   $1,033.50