"Sashimi-grade" is just a marketing term, there are no standard metrics for which fish are graded on their suitability to be eaten raw. Fish markets use the term to describe fish that are processed and stored in a manner to reduce the possibility of parasites. The FDA sets out some guidelines for processing and storage of fish to reduce parasites and you can find them online, but your home freezer won't achieve the recommendations, flash freezing to -31F is the benchmark for wild salmon I believe. Tuna and farmed salmon are the most common "Sushi-grade" fish because they are less likely to contain worms in the first place. Killing worms by cooking requires an internal temperature of at least 145 degrees, salmon dries right out by about 140, so really, any salmon that you would consider eating cooked to less than a disgusting dried out chewy consistency, can be eaten raw with the same level of risk of parasites.