At 1kHz sine wave, the meter is probably the closest to correct (depending on model). 5V is a good level (DMMs tend to develop non-linearity at the bottom of a range).
You can do some experiments to 'characterize' your meter. Wind the frequency up and down to see how the meter reading responds, I would expect that at, say, 50kHz the reading will be well down. The scope reading ought to stay reasonably constant over the 50Hz - 100kHz range, while the meter will probably vary. The reading at 50Hz is probably there the meter will tell the 'truth', so you can get a feel for how close the scope reading is at that point.