How to get a unique numbers for the x position ?

I am trying to get a unique random x position to draw a bitmap, the only problem I have is that the random numbers are very similar. so how to make these unique numbers different from each others by 5 number between each number, the sequence should be like 5 10 15 20 25.

 private String generateXPoistion(String poistion, int numberaOfDigits)
        {
            for(int i=0;i<numberaOfDigits;i++)
            {
                poistion +=  randomGenerator.nextInt(9) + 1;  // the 1 to avoid zero 
            }
            return poistion;
        }
//In the method storeApp, I am using the KeyValue of the hashMap as an x position to draw the bitmap. 

        public void storeApple(Apple apple) 
        {      
            String newId =  generateXPoistion("",3);

                while(appleMap.get(newId) != null )
                {
                    newId = generateXPoistion("",3);
                }
                int foo = Integer.parseInt(newId);
              apple.setPos(foo);
            appleMap.put(newId,apple);
        }