When creating your gig you have to enter it in dollar amounts. It also only lets you select the amount a listbox that shows the values in 5 dollar increments I think. So there’s no way to specify an amount which would equal the GBP amount when creating the gig unfortunately.
You could create a support ticket and suggest it though (suggest they allow GBP values to be entered for gig prices as well as to allow dollar amounts that aren’t 5 dollar multiples - eg. so that you could enter $6.48, the approx current dollar equivalent of £5.00).
You could use a currency converter (eg. google) to convert the amount you want to charge in GBP to USD. But when you enter it in USD in the gig price/package price it has to be in 5 dollar increments). Though you can send offers in 1 dollar increments (as long as it’s not below $5).
if I want to charge £5, should I put $5 and assume it’s a visual bug but does know I’m set to £, or should I adjust pricing to reflect the exchange rate?
The latter - adjust the pricing to reflect the exchange rate. But you can only enter in 5 usd increments.