// normal tax
assert_eq!(
  deduct_tax(&deps.as_mut().querier, Coin::new(50000000u128, "uusd")).unwrap(),
  Coin {
    denom: "uusd".to_string(),
    amount: Uint128::new(49504950u128)
  }
);
(coin.amount.checked_sub(coin.amount.multiply_ratio(
    Uint128::new(1) * tax_rate,
    DECIMAL_FRACTION,
)))?,
