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	$13.77	13.166%	$15.583	$15.58	$15.60	$15.60
Purchase #2	$111.69	10.327%	$123.2242	$123.22	$123.20	$123.20
Purchase #3	$53.40	6.468%	$56.8539	$56.85	$56.85	$56.90
Purchase #4	$24.74	4.617%	$25.8822	$25.88	$25.90	$25.90
Purchase #5	$8.65	13.115%	$9.7844	$9.78	$9.80	$9.80
Purchase #6	$34.70	6.697%	$37.0239	$37.02	$37.00	$37.00
Purchase #7	$192.83	8.544%	$209.3054	$209.31	$209.30	$209.30
7 purchase totals =	$439.78		$477.6570	$477.64	$477.65	$477.70