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 $248.88   5.527%   $262.6356   $262.64   $262.65   $262.60  
  Purchase #2 $70.44   5.650%   $74.4199   $74.42   $74.40   $74.40  
  Purchase #3 $206.45   12.769%   $232.8116   $232.81   $232.80   $232.80  
  Purchase #4 $188.38   7.609%   $202.7138   $202.71   $202.70   $202.70  
  Purchase #5 $196.60   7.266%   $210.885   $210.89   $210.90   $210.90  
  Purchase #6 $140.95   11.182%   $156.711   $156.71   $156.70   $156.70  
  Purchase #7 $109.72   8.394%   $118.9299   $118.93   $118.95   $118.90  
  7 purchase totals = $1,161.42       $1,259.1068   $1,259.11   $1,259.10   $1,259.00