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	$19.74	6.567%	$21.0363	$21.04	$21.05	$21.00
Purchase #2	$228.77	4.162%	$238.2914	$238.29	$238.30	$238.30
Purchase #3	$12.51	7.634%	$13.465	$13.47	$13.45	$13.50
Purchase #4	$52.54	8.249%	$56.874	$56.87	$56.85	$56.90
Purchase #5	$145.60	11.814%	$162.8012	$162.80	$162.80	$162.80
Purchase #6	$133.29	6.215%	$141.574	$141.57	$141.55	$141.60
Purchase #7	$12.53	8.422%	$13.5853	$13.59	$13.60	$13.60
7 purchase totals =	$604.98		$647.6272	$647.63	$647.60	$647.70