Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$77.56	8.639%	$84.2604	$84.26	$84.25	$84.30
Purchase #2	$70.62	11.616%	$78.8232	$78.82	$78.80	$78.80
Purchase #3	$51.50	3.138%	$53.1161	$53.12	$53.10	$53.10
Purchase #4	$50.52	6.676%	$53.8927	$53.89	$53.90	$53.90
Purchase #5	$8.81	13.682%	$10.0154	$10.02	$10.00	$10.00
Purchase #6	$124.77	11.412%	$139.0088	$139.01	$139.00	$139.00
Purchase #7	$154.29	11.556%	$172.1198	$172.12	$172.10	$172.10
7 purchase totals =	$538.07		$591.2364	$591.24	$591.15	$591.20