It certainly doesn't seem grammatically correct. I am unfamiliar with the material but presumably this should be correctly phrased as
0.5 to 0.55 is the upper limit for similar problems
the upper bound for similar problems is between 0.5 and 0.55
As a native English speaker I find the original wording confusing and non-standard.
In a non-mathematical context the phrase does have more common meaning...
as @Dusty says things like "It'll cost you 5 pounds, tops" - meaning it will cost no more than 5 pounds.
Also, "it's the tops" is a somewhat old-fashioned way of saying something is the best. In more modern slang people will say "top" in a context like
"How was the gig?"
"Oh it was top mate"