furthermore -as a more direct answer to the question
a) there’s no provision for that because
b) in 99% of cases (exceptions prove the rule and all that and might work for some prices) it will not be what’s required anyway
assuming you have prices like 9.95, 7.95 and 5.95 if one were to blanket apply 10% you’d end up with 8.96, 7.16, 5.36
I dont think anyone will want these kind of odd prices so you’d have to do most of them manually anyway