The dominant species on this alien planet are sapient, somewhat monstrous bipedal creatures. They possess no eyes at all, are completely blind, and have no concept of vision.

Other senses are as follows:

• Touch: Their tactile senses are equivalent to a human's.
• Hearing: They have sophisticated hearing organs slightly more powerful and capable of more nuance than human ears, especially underwater.
• Smell & Taste: These senses are incredibly powerful and are their primary method of information-gathering. Their entire "face" opens into a fearsome maw (actually a combination mouth/nose orifice) through which they can rapidly sort out detailed information from particles in the air, in a manner akin to the flehmen response, only turned up to 11. They can also derive information underwater by filtering through chemicals in the water (as fish do), without drowning.

For all intents and purposes, the planet is oceanic, with huge diversity of sea-life, and most landmasses having a tropical biome. This species feeds entirely on fruit, vegetables, and seafood.

Civilization is at a tier 6 level, although this answer notes:

. . . the question of discovering mining, chemistry, medicine, etc. is much harder if not impossible if everyone is blind.

So mining, metalworking, and by extension, coin minting is likely to be underdeveloped at best, and nonexistant at worst, unless some condition reasonably exists that could outweigh the developmental hindrance of being blind. (I'm hesitant to just handwave it.)

Under these conditions, what would be a reasonable, reliable form of currency?

Paper notes would be out, as they're primarily vision-based currency. Coins could work, but, as stated above, I'm not sure if their development could be reasonably justified. I've also considered something like shells or coral, but they seem like they'd be too fragile for everyday use.

In summary, the currency needs to be:

• Reasonably obtainable, but not overabundant
• Portable
• Waterproof (Bonus points if it's buoyant, though that's not a necessity)
• Durable enough for everyday use
• Be reliably distinguishable without sight
• Have enough variability for denominations