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	$6.78	10.788%	$7.5114	$7.51	$7.50	$7.50
Purchase #2	$240.93	11.710%	$269.1429	$269.14	$269.15	$269.10
Purchase #3	$139.53	4.287%	$145.5117	$145.51	$145.50	$145.50
Purchase #4	$180.88	5.146%	$190.1881	$190.19	$190.20	$190.20
Purchase #5	$249.36	5.146%	$262.1921	$262.19	$262.20	$262.20
Purchase #6	$62.52	5.872%	$66.1912	$66.19	$66.20	$66.20
Purchase #7	$126.92	6.238%	$134.8373	$134.84	$134.85	$134.80
7 purchase totals =	$1,006.92		$1,075.5747	$1,075.57	$1,075.60	$1,075.50