Do import tariffs tend to increase a country's exchange rate (if so, why)?
Suppose that there is no 45 percent tariff and the market is in some kind of equilibrium. That is the demand for yuans equals the supply of yuans at the current exchange rate.

Now assume Trump does impose a 45 percent tariff. This makes imported Chinese goods in the US more expensive for the American consumer. As a result the consumers will buy fewer Chinese import goods. So far they paid for these goods with dollars and the corporation importing the goods used those dollars to buy yuans and pay for the goods. As a result of the decreased import demand the corporation will want less goods and hence it will buy fewer yuans. Thus decreasing the demand for yuans. The currency exchange market is similar to other markets: If at a price (in this instance this is the USD/CNY exchange rate) the supply outstrips demand the price will decrease. This means that the dollar becomes 'stronger', you will have to pay more yuans to get a dollar.

As a result exports do become somewhat more expensive (in yuans) and imports do become somewhat cheaper (in dollars) until an equilibrium is reached on both the currency and the good markets.