It is incredibly accurate. How much more depends on the type of mission. It is used differently today than in WWII, Korea and even Vietnam. The weapons, such as the 155mm howitzer have been redeveloped several times and the type of ammo has changed. The U.S. Army Airborne is using the 105mm again. It provides tremendous force protection and targeting up to 5-7 miles.
Obviously the use of satellite navigation has improved targeting. Even laying in the guns has become highly sophisticated due to technology.
Plus, the U.S. military is heavily reliant on air power in the modern era (both fixed wing and choppers) for precision targeting. Gone are the days of massive Time on Target raids (for the U.S anyway). There are firebases in Afghanistan that use 155mms (M198). I can't speak in detail on their missions as I'm unsure exactly, but I believe they are mostly supporting Afghan forces and the occasional targets of opportunity.
However, we still massed artillery fire in Syria and other places. The Turkish military as well as Syria's government forces are using 155mm and self-propelled pieces around Aleppo. While the Russians use mostly fighter bombers in Syria, they did supply a lot of towed pieces in the Ukraine to the "rebels" in the Donets basin. Israel has also used self-propelled guns (American made) on southern Lebanon and Gaza the past decade.
I may have given an oversimplification of the issue. My apologies. But for me, I love the topic. Any questions, just let me know.