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	$198.83	13.105%	$224.8867	$224.89	$224.90	$224.90
Purchase #2	$48.84	10.363%	$53.9013	$53.90	$53.90	$53.90
Purchase #3	$148.76	7.613%	$160.0851	$160.09	$160.10	$160.10
Purchase #4	$40.91	6.530%	$43.5814	$43.58	$43.60	$43.60
Purchase #5	$74.50	11.657%	$83.1845	$83.18	$83.20	$83.20
Purchase #6	$96.34	7.310%	$103.3825	$103.38	$103.40	$103.40
Purchase #7	$12.63	8.367%	$13.6868	$13.69	$13.70	$13.70
7 purchase totals =	$620.81		$682.7083	$682.71	$682.80	$682.80