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 $239.90   5.377%   $252.7994   $252.80   $252.80   $252.80  
  Purchase #2 $50.91   7.864%   $54.9136   $54.91   $54.90   $54.90  
  Purchase #3 $70.84   8.447%   $76.8239   $76.82   $76.80   $76.80  
  Purchase #4 $214.69   7.787%   $231.4079   $231.41   $231.40   $231.40  
  Purchase #5 $196.82   4.328%   $205.3384   $205.34   $205.35   $205.30  
  Purchase #6 $168.40   4.475%   $175.9359   $175.94   $175.95   $175.90  
  Purchase #7 $41.55   12.470%   $46.7313   $46.73   $46.75   $46.70  
  7 purchase totals = $983.11       $1,043.9504   $1,043.95   $1,043.95   $1,043.80