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 $185.89   6.602%   $198.1625   $198.16   $198.15   $198.20  
  Purchase #2 $62.99   11.365%   $70.1488   $70.15   $70.15   $70.10  
  Purchase #3 $133.77   13.345%   $151.6216   $151.62   $151.60   $151.60  
  Purchase #4 $234.70   11.808%   $262.4134   $262.41   $262.40   $262.40  
  Purchase #5 $118.43   4.706%   $124.0033   $124.00   $124.00   $124.00  
  Purchase #6 $244.75   11.863%   $273.7847   $273.78   $273.80   $273.80  
  Purchase #7 $136.40   13.349%   $154.608   $154.61   $154.60   $154.60  
  7 purchase totals = $1,116.93       $1,234.7423   $1,234.73   $1,234.70   $1,234.70