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	$143.40	10.510%	$158.4713	$158.47	$158.45	$158.50
Purchase #2	$116.33	6.348%	$123.7146	$123.71	$123.70	$123.70
Purchase #3	$88.61	12.321%	$99.5276	$99.53	$99.55	$99.50
Purchase #4	$152.92	13.591%	$173.7034	$173.70	$173.70	$173.70
Purchase #5	$226.43	4.284%	$236.1303	$236.13	$236.15	$236.10
Purchase #6	$132.49	8.404%	$143.6245	$143.62	$143.60	$143.60
Purchase #7	$169.89	4.630%	$177.7559	$177.76	$177.75	$177.80
7 purchase totals =	$1,030.07		$1,112.9276	$1,112.92	$1,112.90	$1,112.90