=CHOOSE(IF(A1<0.5,1,IF(AND(A1>=0.5,A1<=1),2,3)),10,15,20)

=IF(A1<0.5,10,IF(AND(A1>=0.5,A1<=1),15,20))

=IF(A1<0.5,10,IF(AND(A1>=0.5,A1<=1),15,IF(A1>1,20,"Something else")))

=((A1<0.5)*10)+((A1>=0.5)*15)+((A1>1)*20)

AND(A1>=0.5,A1<=1)

Product  Price
Candy    1
Apples   15
Chicken  21

Product  Quantity
Candy          25
Apples         15
Chicken        10
-----------------
Tax           $37
Total        $497

=E2 * VLOOKUP(D2, $A$2:$B$4, 2, FALSE)

=IF(A1<0.5,10,IF(A1<=1,15,20))