Auto Update Form Fields

[Cross]

Hello,

I'm currently developing a Point of Sale system for my business in PHP. The place I am currently stuck at right now is the invoicing system. What I want to do is this:

1. When someone enters in a product price it will:
a. Be sent to the sub-total form field as will any other product prices.
b. The sub-total is then sent through two form fields for the two types of taxes of 5 and 8 percent.
c. Upon being parsed through the taxes, the final total being displayed in another field.
2. When someone enters in an amount received on the same page, will calculate the change required and be displayed in a form field.

I've looked everywhere for something similar, but to no avail. I know this can be done in JavaScript, but I don't know it well enough.

Any help would be greatly appreciated.
Matt

[akash]

1. When someone enters in a product price it will:
a. Be sent to the sub-total form field as will any other product prices.
b. The sub-total is then sent through two form fields for the two types of taxes of 5 and 8 percent.
c. Upon being parsed through the taxes, the final total being displayed in another field.
2. When someone enters in an amount received on the same page, will calculate the change required and be displayed in a form field.
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