Your customer gets and invoice for, let's say, $143.05. He/she comes in and pays cash. Like an idiot you trust him/her and don't count the money. He/she happily takes the merchandise and leaves. Then you count the money, only to realize he/she gave you $142. Now you owe the boss/owner/manager $1.05. The end of day closing doesn't match the money. You stole some money! Are you blind? You didn't count? .... UNLESS you fix the invoice so that the order + tax is exactly $142. You pick up the calculator and
... unless you are good at math you say, what the hell do I do? , that (customer) is an asshole. They do the same all the time.
(Answer) Make the invoice for $132.71 with 7% tax = $142
You are a freelancer (or similar). You TELL your customer an estimate for the job is $445. The customer likes the price and sends a check for exactly $445. Customer doesn't care about your taxes, only about their price. BUT you still want to keep your accounting in order. You need to fix your invoice so that the actual job + taxes is exactly $445. You pick up the calculator and
... unless you are good at math you say, what the hell do I do? , that customer is an idiot, how can they forget about taxes.
(Answer) Make the invoice for $415.88 with 7% tax = $445