Basically if you know your addition just add the values of each coin or dollar bill. Just forget about the $ sign or cent sign when adding the values together.
FOR EXAMPLE:
$1 and $2.75
You would ignore dollar sign and add together like normal to get
3.75
But remember to add dollar sign back at the end.
If the value only have 2 values with cents it should be something like
0.54 cents BUT NO DOLLAR SIGN
Hope that helps