A sample must not contain more than 2% contaminants to be pure. Are there instances where 2.12% is ok?
It depends mainly on the accuracy of your measuring instrument in practice and the accuracy required by your work.

For example:

If you want to make a solution with 2g solute in it, and to measure amount of solute you have an measuring instrument that have least count of 0.1g, then 2.05g is acceptable as the instrument will show 2.0g only but if the least count of intrument is 0.01g then 2.05g is not acceptable if you want 2g.

In real life the least count varies for different situations.

For example if you are manager of a water bottle manufacturing unit you won't need much accuracy to fortify the water with minerals, but if you are carrying out a titration in lab to find strength of some oxidising agent you need very high accuracy that is why burette are made such accurate.