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	$17.98	5.449%	$18.9597	$18.96	$18.95	$19.00
Purchase #2	$145.90	13.308%	$165.3164	$165.32	$165.30	$165.30
Purchase #3	$135.25	11.743%	$151.1324	$151.13	$151.15	$151.10
Purchase #4	$63.83	6.282%	$67.8398	$67.84	$67.85	$67.80
Purchase #5	$27.44	11.508%	$30.5978	$30.60	$30.60	$30.60
Purchase #6	$40.91	12.667%	$46.0921	$46.09	$46.10	$46.10
Purchase #7	$112.77	12.680%	$127.0692	$127.07	$127.05	$127.10
7 purchase totals =	$544.08		$607.0074	$607.01	$607.00	$607.00