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 $237.65   10.226%   $261.9521   $261.95   $261.95   $262.00  
  Purchase #2 $30.56   10.648%   $33.814   $33.81   $33.80   $33.80  
  Purchase #3 $41.57   5.353%   $43.7952   $43.80   $43.80   $43.80  
  Purchase #4 $186.79   10.533%   $206.4646   $206.46   $206.45   $206.50  
  Purchase #5 $57.69   5.523%   $60.8762   $60.88   $60.90   $60.90  
  Purchase #6 $63.28   9.302%   $69.1663   $69.17   $69.15   $69.20  
  Purchase #7 $228.94   8.227%   $247.7749   $247.77   $247.75   $247.80  
  7 purchase totals = $846.48       $923.8433   $923.84   $923.80   $924.00