Step 1 :First, we need to calculate the unpaid balance at the end of July. This is the initial balance plus the purchases made, minus the payment made. So, the unpaid balance at the end of July is \(1063.40 + 516.16 - 777.43 = 802.13\) dollars.
Step 2 :Next, we calculate the finance charge for the month of July. This is the unpaid balance at the end of July times the monthly interest rate. So, the finance charge is \(802.13 \times 0.0155 = 12.43\) dollars, rounded to the nearest cent.
Step 3 :Finally, we calculate the new balance on the first day of the August billing cycle. This is the unpaid balance at the end of July plus the finance charge. So, the new balance is \(802.13 + 12.43 = \boxed{814.56}\) dollars, rounded to the nearest cent.