If you're looking for a meeting place or a good stop around ½ or halfway between Tacoma and Santa Rosa, CA, you can try Medford, OR, which is about 6½ hours south of Tacoma, or almost 6 hours north of Santa Rosa, CA.
Other possible places to stop near the midpoint include Anchor, Lavadoure, Greenback, Booth, and Grants Pass.
About ¼ or a fourth of the way, you can stop at Salem, OR. This is about 3 hours south of Tacoma.
About ⅓ or a third of the way, you can stop at Eugene, OR. This is about 4 hours south of Tacoma.
About ⅔ or two thirds of the way, you can stop at Hawkinsville, CA. This is almost 8 hours south of Tacoma, or about 4½ hours north of Santa Rosa, CA.
About ¾ or three fourths of the way, you can stop at Redding, CA. This is about 9 hours south of Tacoma, or about 3½ hours north of Santa Rosa, CA.
If you drive straight through without stopping at all, the total distance is 754 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 12 hours, 22 minutes.