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 $231.41   4.853%   $242.6403   $242.64   $242.65   $242.60  
  Purchase #2 $70.53   9.187%   $77.0096   $77.01   $77.00   $77.00  
  Purchase #3 $55.57   7.724%   $59.8622   $59.86   $59.85   $59.90  
  Purchase #4 $94.92   5.463%   $100.1055   $100.11   $100.10   $100.10  
  Purchase #5 $241.59   8.557%   $262.2629   $262.26   $262.25   $262.30  
  Purchase #6 $16.43   7.303%   $17.6299   $17.63   $17.65   $17.60  
  Purchase #7 $166.71   4.662%   $174.482   $174.48   $174.50   $174.50  
  7 purchase totals = $877.16       $933.9924   $933.99   $934.00   $934.00