How Far Back Does a Power of Attorney Need to Keep Records?

In regard to being a power of attorney (PoA), how far back do you have to keep documentation for accounting purposes?

I have been PoA for my mother since 2004 and had to place her in a nursing home due to her dementia 13 months ago; she is now 90 and has enough assets to pay for her care with her private funds for at least a few more years. Because of the the 5-year Medicaid look-back period, I have been discarding all records that go beyond 5 years, and have been doing so on a monthly basis. For example, this month (July 2016) I discarded all records dated June, 2011. Do I need to hold onto everything, no matter how old it is, just in case of an audit (for example, at the request of my siblings) or is 5 years of record keeping sufficient?