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 $193.58   6.382%   $205.9343   $205.93   $205.95   $205.90  
  Purchase #2 $131.77   6.537%   $140.3838   $140.38   $140.40   $140.40  
  Purchase #3 $109.47   5.474%   $115.4624   $115.46   $115.45   $115.50  
  Purchase #4 $237.30   10.792%   $262.9094   $262.91   $262.90   $262.90  
  Purchase #5 $94.76   9.151%   $103.4315   $103.43   $103.45   $103.40  
  Purchase #6 $127.61   11.795%   $142.6616   $142.66   $142.65   $142.70  
  Purchase #7 $59.44   6.226%   $63.1407   $63.14   $63.15   $63.10  
  7 purchase totals = $953.93       $1,033.9237   $1,033.91   $1,033.95   $1,033.90