v = Variables[exp];
Prepend[N[
   Append[v, exp] /. 
    FindInstance[exp < 1/2 && 0 < # < 1 & /@ v , v , 20]], 
  Append[v, "exp"]] // MatrixForm

v = Variables[exp];
Prepend[N[
   Append[v, exp] /. 
    FindInstance[exp < 1/2 && 0 < # < 1 & /@ v , v , 20]], 
  Append[v, "exp"]] // MatrixForm

One way to restrict the results to even 10's is to round and then double check we still meet the criterea.

TableForm[
 Sort@Select[Join[#, {(exp /. Rule @@@ Transpose[{v, #}])}] & /@
    Union[
     Round[v /. 
       FindInstance[(exp /. Subscript[R, n_] :> Subscript[R, n]) < 
            1/2 &&
            0.05 < # < .95 & /@ v , v , 20], .1]] , Last[#] < .5 &], 
 TableHeadings -> {None, Join[v, {"exp"}]}]