Tandem's rhymes with:
memorandums, condoms, memorandums, referendums, adam's, adams, adams', addams, addendums, condoms, fiefdoms, freedom's, freedoms, kingdom's, kingdoms, mcadams, memorandums, modems, needham's, odoms, oldham's, referendums, saddam's, sedums, sheikdoms, wadhams
Tandem's sounds like:
tainting, taunting, tendencies, tendency, tending, tendons, tenting, tomatino's, tontons