Thats a metaphorial way to descripe something is in a great number beyond counting. 牛毛 indicates the thing it described is as much as the hair on cow's skin. I guess 多牛毛的各种税费 should be 多如牛毛的各种税费。如 means 像, as, and be like. The sentence simply means there are as many kinds of taxes as the number of cow's hairs.

这里“牛毛”是一种比喻，形容特别特别多/不计其数, so many just like the fur of cattle 多如牛毛的各种税费是说，各种各样的税费太多了

再插一句，我完全同意以上各位的意见，牛毛这里确实是一种比喻的说法。但是请注意，不是所有表达数量多的地方都可以使用牛毛来做比喻的，用牛毛来打比方的情况据我了解并不是很多。 从词典里查到的词条来看： 牛毛 niú máo 牛身上的毛。形容细而稠密 牛毛细雨 “牛毛细雨”，描绘的是春季的细雨绵绵，这个比喻是行得通的。因为牛毛和细雨在某些外形特征上具有相似之处。著名散文家朱自清的散文《春》中有使用“牛毛”来描写细雨的句子，“雨是最寻常的，一下就是三两天。可别恼，看，像牛毛，像花针，像细丝，密密地斜织着，人家屋顶上全笼着一层薄烟。” 但是从严格意义上讲，“多如牛毛的税费”这个比喻其实并不是非常贴切，因此个人建议不要使用。

牛毛还有 细 的意思 比如说 牛毛细雨 就是说雨下的 很细很小

how many seas must a white dove sail 　　before she sleeps in the sand? how many times must the cannonballs fly before they are forever banned? how many haris must a man count on an ox before you call him a mathematician ? the answer my friend, is showing like this:　　 as many as the hairs on an ox; countless; innumerable .