Tax % on item type sales line changes based on Amount

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When I enter any item on a sales order line, my tax rate should be 5% across the board based on my Tax Area Code. However, the first item I enter (Amount excl Tax = 112.50) changes the Tax % to 5.0044, and the second item line (Amount excl tax = 112.50) Tax % changes to 4.99556. Making the first item amount incl tax 118.13, and the second item amount incl tax is 118.12, even though the Amount and tax rate should be exactly the same.

Oddly, the lower the Amount excl Tax is, the more drastic the Tax % changes. It always balances out among the items to be 5% which makes the overall total correct, but makes the line Amount Incl Tax wrong.

Any ideas what the heck is happening?