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	$225.39	11.636%	$251.6164	$251.62	$251.60	$251.60
Purchase #2	$161.89	13.329%	$183.4683	$183.47	$183.45	$183.50
Purchase #3	$132.49	13.564%	$150.4609	$150.46	$150.45	$150.50
Purchase #4	$170.70	12.558%	$192.1365	$192.14	$192.15	$192.10
Purchase #5	$47.76	5.388%	$50.3333	$50.33	$50.35	$50.30
Purchase #6	$172.87	3.268%	$178.5194	$178.52	$178.50	$178.50
Purchase #7	$45.55	10.491%	$50.3287	$50.33	$50.35	$50.30
7 purchase totals =	$956.65		$1,056.8635	$1,056.87	$1,056.85	$1,056.80