Each time you save as a jpeg it compresses again, unless you are working in a program like the GIMP or photoshop which will keep the original in memory until you close the program.
For most efficient use of the card try just shooting in highest quality jpeg, then when you transfer them to your computer save them as a tiff. From that point always keep saving the files as tiffs, until you produce a version for the web or emailing, at which point export a high quality jpeg.
I highly recommend The GIMP for a powerful free editor that has good jpeg options - I save at 95% quality with the best quality advanced options.
Even better would be to work in RAW, export to tiff if needed for editing, then export final version in jpeg, but if the problem is the conversion to jpeg from your programs then it's sometimes better to start with a high quality jpeg (depends on the jpeg engine of your camera though).