Do the believer's sins continue to be expiated due to the toil, exhaustion, and torment he experiences in the grave, and will his grave then be transformed into a garden, or are there sins that are only forgiven on the Day of Judgment?

Calamities and misfortunes in this world expiate sins, and so does the punishment of the grave. So, when a servant dies, what he experiences in the grave—the tribulation, the compression, and the terror—expiates his misdeeds, and we hope that Allah will deliver him from punishment in the Hereafter.