add choice of plastic bag

Hello, from 1/1/2018 Greece has to charge plastic bags everywhere and i would like to add this choice in my e shop. I would like to create the choice: do you want plastic bag? and two radio buttons with YES or NO and also if it is yes, to add the amount of 0.03€ in total amount. I think i could put it in payment methods . Do you have any ideas? Thank you in advance!

I think i could put it in payment methods .

In the order totals would be the best option to accomplish this.

Do you know what should i write to do this?

Optional Fee/Discount is designed to do this. It's a standard Module extension, so you can place the module in any standard module location (e.g. Column Left/Right or Content Top of the checkout page). Customers can then choose the option and it will add the appropriate fee if selected.

Feel free to take a look at the screenshots and demo site, and if you're interested let me know at www.getclearthinking.com/contact if you have any further questions.