The total cost of the pendant including tax is $703.45
Percentage is always in per 100, the sales tax rate is 10%.
The original price of the pendant is $639 .50
The tax on the pendant will be
10/100 × 639.50
= $63.95
The total cost including tax will be
original cost + tax
= 639.50 + 63.95
= $703.45
Therefore the total of the pendant including tax is $703.45