Again, check out that supposed pronunciation:
I don't know how this could have ever gotten started, because it doesn't match any dictionary, either English or French. Some references, in each case pronouncing the final "s" sound:
- Dictionary.com, including entries from the Random House Dictionary and others -- including an audio link at the top.
- Wiktionary.org: "Some English speakers, aware that some final consonants are dropped in French, overcompensate by dropping the final /s/ sound in grâce, making this sound like French coup de gras ('strike of grease'). This mispronunciation is quickly becoming ubiquitous and is being popularized by the media (e.g., it occurs twice in Quentin Tarantino's Kill Bill Volume 2)." Also includes an audio link.
- Cambridge English Dictionary, with audio link.
- Oxford Dictionary, with audio link.
- Collins English Dictionary.
- Google Translate, with audio link.