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 $228.25   8.222%   $247.0167   $247.02   $247.00   $247.00  
  Purchase #2 $241.66   8.131%   $261.3094   $261.31   $261.30   $261.30  
  Purchase #3 $51.43   3.329%   $53.1421   $53.14   $53.15   $53.10  
  Purchase #4 $188.43   13.661%   $214.1714   $214.17   $214.15   $214.20  
  Purchase #5 $238.63   12.557%   $268.5948   $268.59   $268.60   $268.60  
  Purchase #6 $231.87   4.682%   $242.7262   $242.73   $242.75   $242.70  
  Purchase #7 $143.60   13.558%   $163.0693   $163.07   $163.05   $163.10  
  7 purchase totals = $1,323.87       $1,450.0299   $1,450.03   $1,450.00   $1,450.00