This feeling and perception is more cemented by the slab we use in many areas of our daily life. For example the tax rate may be lower for those coming in the slab 1 to 99 and it will be high fo slab coming from 100 to 999. Most tariffs we pay in our daily life are made in slabs. Say electricity or water .The rate and tariff for a consumption slab of upto 99 will be one and lowest. The slab for 100 to 500 and then 501 t0 999 may be still higher.
Thus it is well imprinted that even the lowest number with higher number of digits is very large than the largest number with the same lower number of digits. Similarly numbers having decimals appear t us as much lower in value that the next higher whole number even if the real difference is a single decimal .
When anyone pays 10 Rs. It feels like a lot. But the cost 9.99 Rs goes to show that they are saving something small. Unless the person is rich enough, people do care for even small penny. And this is another reason why many shopping mall and the online sites make use of the 9 in their pricing. Some also give illusion of 1 free for 3 purchases. And some give 5 for 3 and so on. It depends on how the model is managed for the profit.
'Idhuvum Kadandhu Pogum "
Even this challenging situation would ease