I gave her six pennies 和 It coats only a few pence 中的pennies

pence & pennies are the plural of penny.Pence is used in England and I don't think ever used in Canada/America/Australia where the term "pennies" is used.
Australia no longer has pennies with the smallest coin being 5 cents.1 penny = 1 cent
100 cents = 1 dollar
In England 100 pence = 1 pound
是英美文化的不同.
*pence多指英国的新/旧版的便士的复数.penny做“美分”讲时,一般不用.
*pennies则就是penny的复数,一般来讲,penny的所有释义,不管是便士,还是美分（或任何小面额的硬币）,都可以用pennies.

penny是面值一分的，six pennies就是六个一分的硬币
pence是面值两分及以上的硬币，第二个句子的意思是几分钱