Gradually expiring vouchers

Recently I re-discovered £10-worth of Tesco's loyalty vouchers which I had temporarily forgotten about, and had gone out-of-date by five days. The air was blue in response to my completely disproportionate visceral reaction to this discovery. Tesco's, in my estimation, and due to no fault which could be fairly attributed to them, dropped in esteem by several notches; the well-known units of esteem.

We all know that this is why traders issue vouchers. Their non-redemption by absent-minded dopes such as me gives them a tidy profit. However the cliff-edge of non-redemption is so final that it can seem rather harsh and perhaps.. see above.. dent the loyalty of semi-habitual customers which are supposedly prized so much.

Normal cash is, of course, a mere voucher. The national banks engineer the gradual expiry of cash by means of inflation and little tricks such as periodically changing the coins and notes rendering the ones down the back of the sofa 'Non legal tender'. This, however, is a gradual decline, rather than the ripped-off sticking plaster of fixed expiry date which led to the sharp pang of regret in my basal ganglia. But in this case nobody cares very much.

My idea therefore is for grocery stores or other businesses to issue 'gradually declining vouchers' which lose their value over time, after their nominal extinction date, say 10% per month to be fair.