Land of unified receipts

Snapshot of receipts on my bed :) Now I can finally throw them away ... ;)

One morning while I was hanging around E's place, I noticed a thick wad of receipts on the table... Thought it really strange why someone would keep such good track of his/her expenditures, but found out towards the end of my trip that it's for a purpose prob only peculiar to Taiwan. Ok, so in Taiwan, they apparently have a system of unified sales receipts... Most of the stores I went to issued receipts of the same design, size and length... Then right at the top of the receipt there's an eight digit number which is apparently a chance for you to win some money at a state lottery... On the flip side, there's a mini red grid with the months the receipt was issued, the corresponding day the lottery results would be announced, as well as when to collect the prizes by.
Now now, why is there such a bizarre system in place? According to E, it's for residents to report on their monthly expenditures when they pay taxes, so that the taxable amount is based on consumers' real income (after taking away expenditures). I didn't really get the rationale though cos even though I've yet to join the ranks of taxpayers all along I had the idea individuals pay taxes solely based on income earned... how come got such good deal one. Decided to google a bit and according to some online sources, it's a way for the govt to ensure ppl pay sales taxes. To circumvent the problem of merchants not declaring their sales, this system was put in place such there will be records when consumers request for sales receipts (assuming that they do, given a chance to strike lottery)... Some charities even leave boxes for ppl to drop their receipts and there are actually volunteers who actually help to match the lottery receipts to see if the charities had won something at the lottery... I wonder how many Taiwanese conscientiously keep all their receipts and match them one by one with the lottery results. I think I would be rather pissed if say after tediously matching two months' worth of receipts I find that I did not win anything..... :P