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	$150.31	4.786%	$157.5038	$157.50	$157.50	$157.50
Purchase #2	$225.37	5.736%	$238.2972	$238.30	$238.30	$238.30
Purchase #3	$158.56	9.446%	$173.5376	$173.54	$173.55	$173.50
Purchase #4	$183.85	5.188%	$193.3881	$193.39	$193.40	$193.40
Purchase #5	$144.84	8.817%	$157.6105	$157.61	$157.60	$157.60
Purchase #6	$66.41	4.509%	$69.4044	$69.40	$69.40	$69.40
Purchase #7	$107.55	3.792%	$111.6283	$111.63	$111.65	$111.60
7 purchase totals =	$1,036.89		$1,101.3699	$1,101.37	$1,101.40	$1,101.30