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	$168.89	12.173%	$189.449	$189.45	$189.45	$189.40
Purchase #2	$118.84	7.159%	$127.3478	$127.35	$127.35	$127.30
Purchase #3	$216.26	8.169%	$233.9263	$233.93	$233.95	$233.90
Purchase #4	$76.50	12.198%	$85.8315	$85.83	$85.85	$85.80
Purchase #5	$95.78	4.243%	$99.8439	$99.84	$99.85	$99.80
Purchase #6	$48.87	5.631%	$51.6219	$51.62	$51.60	$51.60
Purchase #7	$78.64	4.380%	$82.0844	$82.08	$82.10	$82.10
7 purchase totals =	$803.78		$870.1048	$870.10	$870.15	$869.90