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	$11.97	11.873%	$13.3912	$13.39	$13.40	$13.40
Purchase #2	$49.87	4.550%	$52.1391	$52.14	$52.15	$52.10
Purchase #3	$39.28	11.790%	$43.9111	$43.91	$43.90	$43.90
Purchase #4	$109.49	8.321%	$118.6007	$118.60	$118.60	$118.60
Purchase #5	$94.84	4.461%	$99.0708	$99.07	$99.05	$99.10
Purchase #6	$11.72	8.189%	$12.6798	$12.68	$12.70	$12.70
Purchase #7	$138.41	10.480%	$152.9154	$152.92	$152.90	$152.90
7 purchase totals =	$455.58		$492.7081	$492.71	$492.70	$492.70