Costs are off by a few pennies against the Google interface - should I worry?

"Rounding" is close to the truth but you can give them the precise version, which lands better. Google reports cost in micros - millionths of a currency unit - so a click that costs 1.234567 is stored exactly. Anything that displays a currency figure has to round somewhere, and Google's interface rounds each row before it adds them up, while a total computed from the raw micros adds first and rounds once. Add a few hundred thousand rows and the two methods drift by pennies. Neither is wrong; they round at different points. Two things worth checking so you can rule out anything real: Timezone. Your account's reporting timezone decides where a day starts. If a comparison spans a month boundary and the two sides disagree about which day a midnight click belongs to, you get a difference far bigger than pennies. Date range. Today is usually partial and still moving, so including it guarantees a mismatch that fixes itself tomorrow. A consistent difference of pennies on five figures is the arithmetic. A difference of pounds is one of the other two, and worth telling us about.