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	$224.33	12.597%	$252.5889	$252.59	$252.60	$252.60
Purchase #2	$34.79	13.589%	$39.5176	$39.52	$39.50	$39.50
Purchase #3	$160.80	13.798%	$182.9872	$182.99	$183.00	$183.00
Purchase #4	$157.28	7.127%	$168.4893	$168.49	$168.50	$168.50
Purchase #5	$47.52	12.548%	$53.4828	$53.48	$53.50	$53.50
Purchase #6	$137.51	10.156%	$151.4755	$151.48	$151.50	$151.50
Purchase #7	$138.47	12.543%	$155.8383	$155.84	$155.85	$155.80
7 purchase totals =	$900.70		$1,004.3796	$1,004.39	$1,004.45	$1,004.40