As I’m doing more research on how long the Singer-Friden MDTS 908 900/9021 registers were around, I found a couple of shots of the grand opening of Sears in Casper, Wyoming. The store opened in 1982 and it appears installed the MDTS system in the new store.
I know Sears moved from the Singer-Friden registers to NCR 2152s in the 1980s. I was thinking it was around this time, but it must have been a little later in the decade. Of the electronic systems used by Sears, the NCR 2152 must have been around the shortest time, because in late 1991 CompuAdd in Texas designed cash registers for the Sears contract.
So, the Singer system was around for more than a decade (most likely with upgrades in the backend), the NCR system probably barely made it a decade, the CompuAdd systems were around for 10 years and the IBM SurePOS registers from the early 2000s are still around in the few remaining stores.
1 See comments around Sears using the Singer 900/902 registers, not 908 as originally reported.