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 $199.55   7.210%   $213.9376   $213.94   $213.95   $213.90  
  Purchase #2 $163.42   11.757%   $182.6333   $182.63   $182.65   $182.60  
  Purchase #3 $30.68   13.241%   $34.7423   $34.74   $34.75   $34.70  
  Purchase #4 $128.66   13.167%   $145.6007   $145.60   $145.60   $145.60  
  Purchase #5 $192.81   10.175%   $212.4284   $212.43   $212.45   $212.40  
  Purchase #6 $131.46   10.779%   $145.6301   $145.63   $145.65   $145.60  
  Purchase #7 $217.74   3.626%   $225.6353   $225.64   $225.65   $225.60  
  7 purchase totals = $1,064.32       $1,160.6077   $1,160.61   $1,160.70   $1,160.40