You likely have an image of your business card in resolution 9x5cm (300 DPI) from Photoshop.
Now how to tile the image to make them fit on A4 page as many times as possible?
Install ImageMagick and use the attached batch script.
It takes the source image, duplicates it to 3x4 grid to make them fit 12 times on one A4 page. They are easy to cut, with borders as guidelines around them.
Just make sure to set the same DPI before printing, to retain the 9x5cm dimensions.