Increase prices in a column by 20 percent

Yah, that won't work. This seems to though. Enter in B1 and copy down the length of the data:

Formula:

=ROUNDUP(A1,0)-0.05

This will take everything from 1 cent over the dollar and round up to the 95 cents. It will also take the even dollar amount down to 96 cents and round it to 95 cents so. $10.00 will become 9.95 as will $9.99 and less.