Can I use a 5% tolerance resistor instead of a 10% tolerance resistor?
Yes, so long as all the other specifications match.

"10% tolerance" on a component simply means that the actual value of the resistor must be within 10% of the specified value. That is, if you measured the actual resistance of a 6.8kΩ ± 10% resistor with a high-precision ohmmeter, you would measure its value as being somewhere between 6.12kΩ and 7.48kΩ.

As such, a 5% tolerance component will also fit the 10% specification: if the value is within 5%, it will certainly be within 10% as well. The lower tolerance just means that its value will be a more exact fit than the original design required!