Niall Ferguson maintains the tax levels were minimal, especially in comparison to the rest of the empire.

But most people assume it was a protest against hike in the tax on tea. In fact the price of the tea in question was exceptionally low, since the British government had just given the East India Company a rebate of the much higher duty free and had to pay only the much lower American duty on arriving in Boston. Tea had never been cheaper in New England. The “Party” was organized not by irate consumers but Boston’s wealthy smugglers, who stood to lose out. Contemporaries were well aware of the absurdity of the ostensible reason for the protest. “Will not posterity be amazed”, wrote one sceptic, “when they are told that the present distraction tool its rise from the parliament’s taking off a shilling duty on a pound of tea, and imposing three pence, and call it a more unaccountable phrenzy, and more disgraceful to the annals of America, than that of the witchcraft?”

I think most would agree however that taxes were just a suitable line to take by the revolutionaries to a "greater" end result or to use as a lever for political or philosophical gains (representation for example). It wasn't the level of taxation but that it was done unilaterally.

As an aside, whilst niall is controversial with his conclusions, his sources are as accurate as anyone's.

Niall Ferguson - Empire

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If you are looking for %'s its hard as items were taxed individually and at different rates in each colony, with only one state having an income tax of 1%

Per capita tax rates for an Briton were on average 10 times as much as an average American in 1739. This was before the sugar tax was introduced (and then repealed when so unpopular) which tried to even out this imbalance and pay for the war.

Alvin Rabushka - Taxation in Colonial America.