As an experienced editor of American English, I can tell you that this idea of ‘that sounds right’ as being the way to decide correct usage is incredibly flawed. Why guess when you have so many resources available?
From http://www.grammarbook.com/grammar/subjectVerbAgree.asp
[quote]Rule 13
Use a singular verb with sums of money or periods of time.
Examples:
Ten dollars is a high price to pay.
Five years is the maximum sentence for that offense.[/quote]
http://www.sparknotes.com/testprep/books/act/chapter5section2.rhtml
From the main style resource for American English, The Chicago Manual of Style:
[quote]9.21 Words versus monetary symbols and numerals
Isolated references to amounts of money are spelled out for whole numbers of one hundred or less, in accordance with the general principle presented in 9.2. See also 9.3.
seventy-five cents = 75¢
fifteen dollars = $15
seventy-five pounds = £75
Whole amounts expressed numerically should include zeros and a decimal point only when they appear in the same context with fractional amounts (see also 9.19). Note the singular verb in the second example.
Children can ride for seventy-five cents.
The eighty-three dollars was quickly spent.
The instructor charged €125 per lesson.
Prices ranged from $0.95 up to $10.00.
For larger amounts, see 9.25[/quote]
And from the CMoS Web site Q&A:
[quote]Usage
Q. Hello, CMOS Gurus—I cannot seem to locate the rule that proves (or disproves, I guess) the following to be correct: More than 28 million pounds of scrap is reclaimed every year. I thought that units of measurement or money took a singular verb, not plural (such as, three million dollars is a lot, or five miles is a long way). Are there other quantities that this applies to (such as years)? Or am I wrong entirely and should all three of my examples above take a plural verb? —A stumped copyeditor
A. For measures or money or any other quantities, when the items form a whole that isn’t meant to be divided, use a singular verb, as you have. When items are meant to be individual and countable, use a plural verb: Five hundred million Twinkies are produced each year. Since your scrap isn’t being reclaimed one pound at a time, “is” is the right choice.[/quote]
http://www.chicagomanualofstyle.org/CMS_FAQ/Usage/Usage79.html