You are lucky to have variations that small.
Some variation in the grid voltage is inevitable because of how these things work. Wires have resistance, transformers are less than ideal, the load varies. The less variation one allows, the more expensive the grid will be and those expenses inevitably will land in the electric bill, so compromises are made.
I live in Europe where the electrical grid was started years after the US one and a lot of things that Edison (100v that later become 110, 115 and 120) and Westinghouse got wrong were fixed before it was too late to change anything. Our grid voltage is standardized at twice the US one exactly in order to lessen the variations because of the changing load.
The law here mandates your wall socket voltage within 10% from its nominal value (230v). It was 15% not so long ago (say, 20 years) and the nominal value was 220. The new norm (10% around 230v) fits perfectly in the old norm (15% around 220v). I am not sure how exactly it is in the US right now, but one can divide EU voltages by 2 and get (roughly) the evolution of the US grid voltage standard. In Japan, their nominal 100v allows for only 5% variation and they have their very own higher electricity bills to pay.
Most electronic devices (computers, TV-sets, modern inverter-type AC units, etc) have switching-mode power supply unit that is very efficient at changing its internal mode of working in order to keep its output voltage steady when the input voltage changes. And because many of them are marketed world-wide, they are made to accept anything between 100-240v (nominal) plus 10% above and below in order to work world-wide.
Or the market is split to US-type (including Japan so 100-120v plus variation) and EU type (200-240v plus variation) and the power supply units get a bit cheaper at the cost of complexified logistics.
That's why your 116-121 or so volts is completely a non-issue.
There is another group of devices (space heaters, incandescent light bulbs, some modern, but cheap LED lighting devices, cooking appliances, power tools, etc, ...) that don't have any internal stabilization means. Their performance varies a bit (say, +/-20% for +/-10% variation of the voltage) and this is simply considered normal.
And finally, there is a third group of devices - precise scientific/measurement equipment, old tube-based electronics, etc... that are as picky to the power voltage as it gets. If you own and operate one, you probably already know what to do in order to get it working right. Including, but not limited to using it only at night or employing some voltage stabilizer.