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	$40.89	3.736%	$42.4177	$42.42	$42.40	$42.40
Purchase #2	$106.54	5.209%	$112.0897	$112.09	$112.10	$112.10
Purchase #3	$200.60	4.823%	$210.2749	$210.27	$210.25	$210.30
Purchase #4	$235.77	6.688%	$251.5383	$251.54	$251.55	$251.50
Purchase #5	$228.91	10.619%	$253.218	$253.22	$253.20	$253.20
Purchase #6	$38.63	5.178%	$40.6303	$40.63	$40.65	$40.60
Purchase #7	$43.58	7.587%	$46.8864	$46.89	$46.90	$46.90
7 purchase totals =	$894.92		$957.0553	$957.06	$957.05	$957.00