How do firms charge their price when they are in Bertrand competition?

For example, if firm A has a marginal cost of $10, firm B has a marginal cost of $8 and firm C has a marginal cost of $6.

Assuming all firms have the same fixed costs and their strategy is to be in a Nash equilibrium, do firms charge their price equals to the marginal cost or at the point where MC=MR?

What happens if the inverse demand function for all firms is P = 10 Q?