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	$154.91	12.243%	$173.8756	$173.88	$173.90	$173.90
Purchase #2	$18.39	11.566%	$20.517	$20.52	$20.50	$20.50
Purchase #3	$222.65	10.186%	$245.3291	$245.33	$245.35	$245.30
Purchase #4	$22.52	8.766%	$24.4941	$24.49	$24.50	$24.50
Purchase #5	$61.74	6.111%	$65.5129	$65.51	$65.50	$65.50
Purchase #6	$192.41	13.255%	$217.9139	$217.91	$217.90	$217.90
Purchase #7	$122.33	4.569%	$127.9193	$127.92	$127.90	$127.90
7 purchase totals =	$794.95		$875.5619	$875.56	$875.55	$875.50