If it's claimed you looted the petty cash of the full $5.88 (and you didn't), then go ahead and make your denial, even absent the name of your accuser. It's likely that you'd remember knocking off the office till.
But when the accuser's identity is missing it's usually the first of several gaps.
What if it's alleged that you "insulted" your accuser: No name of the accuser, words spoken, time, date, or location? Natural Justice has flown, and the presumption of innocence as well. (If you imagine the example far-fetched, I'm happy for your innocence.)
If the absence of relevant information makes it difficult or impossible to reply with certainty, don't. Don't presume, speculate or guess. Invoke your right to Natural Justice and take a break. It's time for professional advice.
It's my experience that human resource professionals know the unfairness inherent in such situations. Some, unfortunately, are powerless to prevent them; and a few, I fear, revel in it. ▪
Have you ever seen a sign on the roadway reading:
'This is not the road to the airport.'
Those who know the system cannot imagine
the problems facing those who do not.
—Edward de Bono (b. 1933)