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	$17.25	4.262%	$17.9852	$17.99	$18.00	$18.00
Purchase #2	$79.84	11.676%	$89.1621	$89.16	$89.15	$89.20
Purchase #3	$53.95	4.199%	$56.2154	$56.22	$56.20	$56.20
Purchase #4	$243.94	6.716%	$260.323	$260.32	$260.30	$260.30
Purchase #5	$46.78	3.420%	$48.3799	$48.38	$48.40	$48.40
Purchase #6	$112.63	3.583%	$116.6655	$116.67	$116.65	$116.70
Purchase #7	$90.83	9.851%	$99.7777	$99.78	$99.80	$99.80
7 purchase totals =	$645.22		$688.5088	$688.52	$688.50	$688.60