Its really heavy to give a correct answer, if you don't show us the context where the for loop is used. But I'll try:

There should be a part in the void loop method where you detect that the "bankValue" is down to zero. Like:

if (bankValue == 0) 
{ 

}

First you must be sure that, the for loop is called within this block.

if (bankValue == 0) 
{ 
  // I corrected the loop to run exact 5 times (<= -> <)
  for (int i = 0; i < 5; i++) 
  {
    led HIGH
    delay(500);
    led LOW
    delay(500);
  }
}

Then you need a flag int blinkingDone = 0; to indicate that the for loop has executed. This flag must be initialize with a falsy value, set to trueish after the loop is done and reset if the user "fills" the bankValue again.

Then you could use it as a guard to enter the for loop. Like:

int blinkingDone = 0;
int bankValue = 0;

..... somewhere else

if ( coin inserted or so )
{
  // fill bankValue
  blinkingDone = 0;
} 

..... somewhere else 

if (bankValue == zero && ! blinkingDone) 
{ 
  // I corrected the loop to run exact 5 times (<= -> <)
  for (int i = 0; i < 5; i++) 
  {
    // led HIGH
    delay(500);
    // led LOW
    delay(500);
  }
  blinkingDone = 1;
}

There are potential better ways to do it. But I don't know your code. So this is the simplest way I can imagine.

Its really heavy to give a correct answer, if you don't show us the context where the for loop is used. But I'll try:

There should be a part in the void loop method where you detect that the "bankValue" is down to zero. Like:

if (bankValue == 0) 
{ 

}

First you must be sure that, the for loop is called within this block.

if (bankValue == 0) 
{ 
  // I corrected the loop to run exact 5 times (<= -> <)
  for (int i = 0; i < 5; i++) 
  {
    led HIGH
    delay(500);
    led LOW
    delay(500);
  }
}

Then you need a flag int blinkingDone = 0; to indicate that the for loop has executed. This flag must be initialize with a falsy value, set to trueish after the loop is done and reset if the user "fills" the bankValue again.

Then you could use it as a guard to enter the for loop. Like:

int blinkingDone = 0;
int bankValue = 0;

..... somewhere else

if ( coin inserted or so )
{
  // fill bankValue
  blinkingDone = 0;
} 

..... somewhere else 

if (bankValue == 0 && ! blinkingDone) 
{ 
  // I corrected the loop to run exact 5 times (<= -> <)
  for (int i = 0; i < 5; i++) 
  {
    // led HIGH
    delay(500);
    // led LOW
    delay(500);
  }
  blinkingDone = 1;
}

There are potential better ways to do it. But I don't know your code. So this is the simplest way I can imagine.