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 $60.60   13.416%   $68.7301   $68.73   $68.75   $68.70  
  Purchase #2 $78.64   11.540%   $87.7151   $87.72   $87.70   $87.70  
  Purchase #3 $231.48   13.489%   $262.7043   $262.70   $262.70   $262.70  
  Purchase #4 $92.85   11.189%   $103.239   $103.24   $103.25   $103.20  
  Purchase #5 $242.76   6.791%   $259.2458   $259.25   $259.25   $259.20  
  Purchase #6 $53.43   13.468%   $60.626   $60.63   $60.65   $60.60  
  Purchase #7 $119.83   3.560%   $124.0959   $124.10   $124.10   $124.10  
  7 purchase totals = $879.59       $966.3562   $966.37   $966.40   $966.20