Possible Clues:

• Penny, and what advances in position through this puzzle's four longest answers
• Penny value
• Coin cast using carbon -- not shilling
• Limits cell development for a change in Ireland
• Coin that some wish to abolish
• Phased-out Canadian coin
• Certified accountant sides with copper
• Copper that's mostly zinc
• Change jar clinker
• Small change, and a word that can follow the first parts of 18-, 25-, 43- and 58-Across