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	$88.83	12.255%	$99.7161	$99.72	$99.70	$99.70
Purchase #2	$65.37	10.789%	$72.4228	$72.42	$72.40	$72.40
Purchase #3	$107.72	6.525%	$114.7487	$114.75	$114.75	$114.70
Purchase #4	$19.65	7.131%	$21.0512	$21.05	$21.05	$21.10
Purchase #5	$31.83	10.526%	$35.1804	$35.18	$35.20	$35.20
Purchase #6	$75.62	13.566%	$85.8786	$85.88	$85.90	$85.90
Purchase #7	$228.59	10.514%	$252.624	$252.62	$252.60	$252.60
7 purchase totals =	$617.61		$681.6218	$681.62	$681.60	$681.60