Accuracy is a relative term. It depends on how much accuracy you need. More accuracy than you need doesn't return anything for the added cost. How big is the IR source and how big is the box you are picking it up with?
For the robots - you do some testing to determine the repeatability of moves and add some fudge factor and it comes out close enough (generally that is what is meant by accuracy - is it close enough to work under the required conditions. Does that machined part need to be within 1", or 1/4" or 0.005" or 0.0005". More precision costs more money and time.) A pulse or 2 (or 4 or 8)for every revolution of the motor may work and also doesn't require a lot of processor overhead. An encoder requires more overhead and may require the rest of the process run slower. Whats the goal? to get there and back, or get tehere and backe the fastest?
Since all you have to measure from is the wheels, then you have to figure out how to keepthe slipage down. Things like don't accelerate too fast and slip the wheels. FIgure out the best way to corner. Is it better to stop one wheel and pivot around it, or is it better to keep the inside wheel turning slowly so it sticks better? Do you also know the measurements of the maze? you can use bumps of the maze to reset position info and correct for slippage.