Just for clarity, this is not a general question on simple present tense, but a question specific to the sentences:
"Ten pennies are a dime"
"Ten pennies is a dime"
I asked a math teacher and he said ten pennies was(were?) a 'set,' singular and thus 'is' was correct. It was an interesting explanation, coming from a math teacher, but I am still leaning towards the rule of using simple present tense with singular or plural subjects.
Maybe I've answered my own question, but "Ten pennies is a dime" still sounds like the correct answer, even though it would appear to contradict the rule for using simple present tense.
Any thoughts or insight would be greatly appreciated.