In most cases, if the subject and verb do not agree then we have a grammatical error, as in the following examples:
My friend have a dog.
I never eats cheese.
However, there are cases where semantics overrides the usual agreement rules. This often occurs with collective nouns:
The committee have decided to disband.
The team are not playing very well.
In such cases the speaker conceptualises the committee or team in terms of their members.
The opposite occurs in examples such as:
Three weeks seems a long time.
Here's ten dollars.
Two eggs is plenty.
According to the Cambridge Grammar of the English Language (p504):
... here an NP (noun phrase) that is formally plural is conceptualised
as referring to a single measure (of time, money, distance, or
whatever) and accordingly takes a singular verb. The measure override
is characteristically found with be or other complex-intransitive verbs such