I dont know what the law is in Bangalore, but using a Taximeter that has not met the required standards in the UK is a very serious offence.
I have designed a few taximeters now, and I could save myself an absolute fortune by building my own (I fit taximeters as my job) but the cost of meeting the regulations (including sending several away to be tested (to destruction in some cases) at your own expense) and the latest european EMI regulations for vehicle electronics now in force - it is totally pointless, the red tape would bankrupt me - so I just buy them from the worlds largest manufacturer of taximeters. (On a side note, in most of the world the meter must include tamper seals, which must be integral to the casing of the meter too - which means a custom enclosure too)
Unless this is a school project, or a one-off just to prove you can do it - then dont bother - invest your time elsewhere and buy a meter off eBay (or i'll sell you one if you want!)
EDIT: As Bill stated above, none of the pics interface directly with 7Seg LED displays, but the MAX7219 or mabey one of there newer ones will drive your displays (including the hired, stopped, for hire - leds, if your clever with your layout) the MAX7219 will use just 3pins on whichever pic you choose