To find the total amount Maggie will pay for the shirts, we first need to calculate the total cost of the shirts before tax.
The cost of one shirt is $8.50, and she is buying 2 shirts, so:
\[ \text{Total cost of shirts} = 2 \times 8.50 = 17.00 \]
Next, we need to calculate the sales tax. The sales tax is 6.5%, which can be written as 0.065. To find the sales tax amount, we multiply the total cost of the shirts by the sales tax rate:
\[ \text{Sales tax} = 17.00 \times 0.065 = 1.105 \]
Now we can find the total amount paid by adding the sales tax to the total cost of the shirts:
\[ \text{Total amount} = 17.00 + 1.105 = 18.105 \]
Finally, we round this to two decimal places:
\[ \text{Total amount rounded} = 18.11 \]
Thus, the total Maggie will pay for the shirts is:
\[ \boxed{18.11} \]