Adding my two cents. I figured out by you can control the decimal points by using the following code:
hover.tooltips = [ ("Days", "@x{int}"), # this will show integer, even if x is float ("Return", "@y{1.11}"), # this will format as 2-decimal float]
Hope this helps.
Aha! Using @ instead of $ works.
hover.tooltips = [ ("Days", "@x"), ("Return", "@y"),]