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	$234.83	8.605%	$255.0371	$255.04	$255.05	$255.00
Purchase #2	$84.27	10.807%	$93.3771	$93.38	$93.40	$93.40
Purchase #3	$189.83	4.466%	$198.3078	$198.31	$198.30	$198.30
Purchase #4	$128.99	7.429%	$138.5727	$138.57	$138.55	$138.60
Purchase #5	$132.37	13.213%	$149.86	$149.86	$149.85	$149.90
Purchase #6	$121.91	4.622%	$127.5447	$127.54	$127.55	$127.50
Purchase #7	$91.30	12.241%	$102.476	$102.48	$102.50	$102.50
7 purchase totals =	$983.50		$1,065.1754	$1,065.18	$1,065.20	$1,065.20