Hugs! I had a similar situation when I took my dysgraphic son out of public school. He was damaged from his PS experience and doing school at home didn't automatically fix the problem.
Some things that worked:
--taking a few months to decompress and let my son learn the ways he was happy learning: reading, discussing, computer work, documentaries, museums, music, science labs
--number flash cards to work out math problems with instead of paper and pencil
--switching from Saxon to Singapore math because it had way less problems per lesson but they were challenging and my son responded well to them
--math video games
--doing as much out loud as possible
--large square graph paper to line up math problems on
--accepting that fill in the blank worksheets are really a bane to my creative son (They are kind of boring and insulting to an intelligent kid if you think about it)
--giving him blank books, but not requiring him to do anything with them (eventually he asked to write a story with them and now he is a prolific writer!)
--ditching as many worksheets as possible. My son wouldn't do them, but he would do more challenging open ended assignments. So instead of a science review worksheet, I give him a piece of graph paper and her he writes out a few sentences about what he learns and draws a diagram, or makes a comic to go with his writing.
--short lessons (look up Charlotte Mason short lessons)
--anything Charlotte Mason inspired
I enjoyed this article about homeschooling to a child's strengths, and I think it's worth a read.
You can discreetly skip the rounding lesson and subsequent review problems for awhile and go back after a few months. My son did the same thing with number lines and I was like, "Really, number lines?" A half a year later the concept fell into place and I didn't even have to teach it.
Good luck! It's hard, but not impossible. It gets better. Pray for patience. It's OK to get behind in math. We got behind and now we are caught up finally! Just in time for pre-algebra!