Adding money can be tricky for students if they don't have solid mental calculation skills. One way to make it easier for students, is to show them that simply by breaking down coin amounts into multiples of 10c, they can add totals together by simply skip counting by 10s!
My Year 2 students love this activity as it is broken down in simple terms for them. Extension to this activity can be showing students the correlation between cents and dollars. For example, if they skip count the box amounts to a total of 190cents, that is the same as $1.90.
There are 2 worksheets (which I enlarge to A3 size and copy back-to-back). The 3rd slide is Australian coin clipart, which you can use for a multitude of other coin related activities! :)