0.05 x 120 = 6
0.05 x 480 = 24
0.05 x 2,240 = 112
0.05 x 12,500 = 625
5% sales tax is the same as 0.05 numerically, just like 10% is 0.1, 20% is 0.2, 50% is 0.5, etc. You just take that decimal and multiply by the price to get your answer.
I hope this helps :)