What do pennies (or pence) have to do with imperial units? A penny is exactly 1/100 of one pound sterling or GBP 0.01, which is a nice metric style power of ten division of the larger unit. If you want monetary units more congruent with imperial, then you may be thinking of l.s.d. or librae, solidae and denarius - pounds, shillings and pence - with twelve pennies to the shilling. Note this is UK only, I don't think the USA ever had non decimal currency?