When a verb in a quotation does not fit syntactically into your sentence, you may use brackets to change the tense:

If Charles Dickens were alive today, he would likely say, “It [is] the best of times, it [is] the worst of times” (5).

Work Cited

Dickens, Charles. A Tale of Two Cities. Updated and rev. ed., Penguin Classics, 2003.

Brackets can be distracting to your reader, though, so it is often better to revise:

In 1859, Charles Dickens wrote in A Tale of Two Cities, “It was the best of times, it was the worst of times” (5). If he were alive today, he would likely make a similar comment about our era.