Oh, dude, rounding numbers, like, totally takes me back to elementary school. So, 90 rounded to the nearest 10 is... drumroll, please... 90! Yeah, no need to change a thing there. It's already snug as a bug in a rug at 90.
When rounding 90 to the nearest 10, you look at the digit in the tens place, which is 9. Since 9 is closer to 10 than to 0, you round up to the nearest 10. Therefore, 90 rounded to the nearest 10 is 100.