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	$19.45	12.669%	$21.9141	$21.91	$21.90	$21.90
Purchase #2	$63.51	7.425%	$68.2256	$68.23	$68.25	$68.20
Purchase #3	$106.74	4.783%	$111.8454	$111.85	$111.85	$111.80
Purchase #4	$12.89	5.288%	$13.5716	$13.57	$13.55	$13.60
Purchase #5	$96.76	8.484%	$104.9691	$104.97	$104.95	$105.00
Purchase #6	$243.53	9.461%	$266.5704	$266.57	$266.55	$266.60
Purchase #7	$99.68	5.716%	$105.3777	$105.38	$105.40	$105.40
7 purchase totals =	$642.56		$692.4739	$692.48	$692.45	$692.50