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	$123.72	11.146%	$137.5098	$137.51	$137.50	$137.50
Purchase #2	$33.62	8.846%	$36.594	$36.59	$36.60	$36.60
Purchase #3	$90.66	10.136%	$99.8493	$99.85	$99.85	$99.80
Purchase #4	$238.28	9.155%	$260.0945	$260.09	$260.10	$260.10
Purchase #5	$167.87	6.143%	$178.1823	$178.18	$178.20	$178.20
Purchase #6	$51.39	3.247%	$53.0586	$53.06	$53.05	$53.10
Purchase #7	$241.63	3.734%	$250.6525	$250.65	$250.65	$250.70
7 purchase totals =	$947.17		$1,015.9410	$1,015.93	$1,015.95	$1,016.00