With the same size and very similar colours of the $1, $2 and $20 I'm not at all surprised people can be confused. I don't know how blind people cope.

They could make a $2 coin. It would fit in with other Western countries' highest-value circulating coins:

  2 GBP = $2.53
  2 AUD = $1.40
  2 CAD = $1.47
 20 DKK = $3.10
 20 SEK = $2.20
 20 NOK = $2.20
  2 EUR = $2.29
 50 CZK = $2.54
 10 HKD = $1.29
  2 NZD = $1.31
 500JPY = $4.67

That said, other than selling an item second-hand, I haven't used any cash at all since February.