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	$234.46	10.763%	$259.6949	$259.69	$259.70	$259.70
Purchase #2	$242.62	8.323%	$262.8133	$262.81	$262.80	$262.80
Purchase #3	$186.48	11.856%	$208.5891	$208.59	$208.60	$208.60
Purchase #4	$93.85	3.277%	$96.9255	$96.93	$96.95	$96.90
Purchase #5	$226.81	11.575%	$253.0633	$253.06	$253.05	$253.10
Purchase #6	$99.64	12.783%	$112.377	$112.38	$112.40	$112.40
Purchase #7	$27.64	3.188%	$28.5212	$28.52	$28.50	$28.50
7 purchase totals =	$1,111.50		$1,221.9843	$1,221.98	$1,222.00	$1,222.00