Rounding error in checkout

Hi!

There seems to be a rounding error when getting to the checkout page of woocommerce, where the payson plugin shows the total cost and asks for the customer details.
I’ve tested it with the following values -> results:
90 -> 90
91 -> 90.80
92 -> 91.60
93 -> 93.40
94 -> 94.20
95 -> 95
96 -> 95.80
100 -> 100
101 -> 100.80

It seems that multiples of 5 are fine, but for other values there’s a rounding error. Would be nice if this could be fixed as it confuses customers.

PaysonCheckout 2.0 for WooCommerce: 1.2.3
Woocommerce: 3.3.5
Wordpress: 4.9.5