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	$172.31	6.373%	$183.2913	$183.29	$183.30	$183.30
Purchase #2	$61.74	6.619%	$65.8266	$65.83	$65.85	$65.80
Purchase #3	$209.25	3.845%	$217.2957	$217.30	$217.30	$217.30
Purchase #4	$240.50	10.620%	$266.0411	$266.04	$266.05	$266.00
Purchase #5	$120.65	5.669%	$127.4896	$127.49	$127.50	$127.50
Purchase #6	$45.64	5.554%	$48.1748	$48.17	$48.15	$48.20
Purchase #7	$180.78	6.380%	$192.3138	$192.31	$192.30	$192.30
7 purchase totals =	$1,030.87		$1,100.4329	$1,100.43	$1,100.45	$1,100.40