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	$73.86	11.730%	$82.5238	$82.52	$82.50	$82.50
Purchase #2	$100.39	13.862%	$114.3061	$114.31	$114.30	$114.30
Purchase #3	$220.90	13.203%	$250.0654	$250.07	$250.05	$250.10
Purchase #4	$58.92	12.692%	$66.3981	$66.40	$66.40	$66.40
Purchase #5	$155.55	4.608%	$162.7177	$162.72	$162.70	$162.70
Purchase #6	$242.28	3.638%	$251.0941	$251.09	$251.10	$251.10
Purchase #7	$40.56	6.108%	$43.0374	$43.04	$43.05	$43.00
7 purchase totals =	$892.46		$970.1426	$970.15	$970.10	$970.10