Currency

Coinage across The multiverse is, despite the wildly varied sources, relatively standardized. This standardization began not in the Prime Material Plane where most mortals live, but instead in the city of Sigil shortly after its founding. As the people of Sigil began connecting and trading with the various outer and elemental planes they needed a standard unit of their own to use as a point of conversion among the various people. They found a small set of five metals to use as coinage. Each of these metals were widely available in the various outer planes in varying amounts, but each plane in existence had these metals and so they were convenient milestones.
Once these five metals were chosen, thorough testing was performed in regards to the cost of components to arcane rituals. The weight of a god coin, in particular, was chosen so that prices of various spells could easily be expressed in large round numbers. This created a nice central frame of reference which was well understood by the denizens of every plane. The traders of Sigil did not need to say "I want 500 gold"; instead they could say "I want just enough gold to purchase a gem suitable for the raise dead spell". Sigil minted their own coinage in these measurements for use within the city, which gradually made its way throughout the rest of The multiverse.
Over time, other planes began to match the same standards, or indeed set their own standards using very similar units. While coinage is minted in various shapes and sizes by every plane and governing body, this use of magical spells as a central frame of reference quickly gained popularity among traders. This turned modern day coinage into a de facto standard long before the various governments began to formally codify these units in their laws. Even once the events of Ragnarok caused Sigil itself to be disconnected from the other planes, the same standards were already set and had proven to be a convenient enough standard to be used by people in all planes.
The conversion rates are as follows:

Coin	CP	SP	EP	GP	PP
Copper	1	10	50	100	1000
Silver	1/10	1	5	10	100
Electrum	1/50	1/5	1	2	20
Gold	1/100	1/10	1/2	1	10
Platinum	1/1000	1/100	1/20	1/10	1