Sounds to me as if you need to generate a PDF of what you’re wanting to print and have it displayed in their web browser and then they have the option to print. But like said earlier the user will need to select the correct printer to print it to.
Yes Stephen, or a simpler method than pdf I mentioned above is on the thank you page at the end of your transaction you can have a print only stylesheet that hides all the content shown to the screen and shows a different set of content to the printer which contains your receipt formatted for the receipt printer. If this is B2B and you dont mind about doing this to a regular customer visitor you can have a piece of javascript that automatically opens the print dialog to remind the employee to print the receipt (you cant get it to auto-print)
If he make server side app as service (which controls from web gui) to do printing contents then he don’t need maskared print dialog prompt since then server side app which works as service will do a printing process or any other process aka generate pdf or do any other process…
Easiest way to handle this on Windows platform is to make service app as ActiveX Dll or ActiveX EXE as COM+ object which will be then called from server side script like is ASP, ASP.NET, PHP and so on.