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	$19.58	9.589%	$21.4575	$21.46	$21.45	$21.50
Purchase #2	$107.94	9.392%	$118.0777	$118.08	$118.10	$118.10
Purchase #3	$142.98	10.167%	$157.5168	$157.52	$157.50	$157.50
Purchase #4	$10.35	12.211%	$11.6138	$11.61	$11.60	$11.60
Purchase #5	$85.79	4.204%	$89.3966	$89.40	$89.40	$89.40
Purchase #6	$5.74	3.819%	$5.9592	$5.96	$5.95	$6.00
Purchase #7	$11.94	3.468%	$12.3541	$12.35	$12.35	$12.40
7 purchase totals =	$384.32		$416.3757	$416.38	$416.35	$416.50