In the following topology, two 0.68 ohm resistors are paralleled to result in 0.34 ohm for sensing the source current. Can I use three paralleled 1 ohm resistors to result in 0.333 ohm? Does this little difference make any problem? I have to say that 5% tolerance parts were chosen in the coresponding bill of material while I've selected 1% tolerance 1 ohm resistors.
Besides the fact that your 1/3 Ω ±1% resistance is close enough (within the tolerance of the 0.34 Ω ±5% given), the exact value of the sense resistor is not typically critical in this type of converter. This appears to be a type of current-mode boost converter, and what the resistor does is set the maximum current through the inductor. Unless you're operating right on the edge of saturation (generally a bad idea), a small amount more or less current isn't going to cause any problems.
Just ensure that there's enough current to supply your output, and not so much that the inductor saturates or the switches fry, and you should be fine.
That should be perfectly fine. Your intuition is correct.
