I am making a rfid based toll collection system using
Arduino Nano. Can anyone give me the sketch file.
Please............ 
You'll probably be more likely to get the sketch if you provide more details.
Do you have any particular hardware specifications, such as the RFID reader?
How do you want the system to work?
I am using RM-18 Card reader and lcd1602 and arduino nano
Does the LCD have the I2C module like this:
Or is it like this:
And you still haven't provided near enough details.
To be clear, I'm not interested in the gig. I've never worked with RFID and don't own the hardware. I'm just trying to help you get the project specification to the point where someone else could even get started.
Pranesh_Senthilvel has indicated they are using the LCD with the I2C module.
You still haven't provided the rest of the details.
(deleted)
I guess this is a school project. Some of the following has already been said:
Your first have to specify what the system has to do apart from the obvious function of reading an RFID tag.
Things like registering the tag, counting the number of reads, printing out the number of reads per tag in a time period etc. etc. Add in any other constraints like say the user registration database is remote, it has to be powered by batteries etc. etc.
You have to make a list of the hardware (exact specification), identify libraries required. etc. etc. and draw a schematic diagram.
Then plan writing the sketch (or sketches if more than one MPU is required).
If it is a school project, your learning experience will be enhanced if you don't simply pay someone else to do it all for you.