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	$99.92	12.203%	$112.1132	$112.11	$112.10	$112.10
Purchase #2	$59.83	3.156%	$61.7182	$61.72	$61.70	$61.70
Purchase #3	$248.65	12.435%	$279.5696	$279.57	$279.55	$279.60
Purchase #4	$82.46	8.371%	$89.3627	$89.36	$89.35	$89.40
Purchase #5	$226.60	12.248%	$254.354	$254.35	$254.35	$254.40
Purchase #6	$78.43	11.171%	$87.1914	$87.19	$87.20	$87.20
Purchase #7	$138.29	12.777%	$155.9593	$155.96	$155.95	$156.00
7 purchase totals =	$934.18		$1,040.2684	$1,040.26	$1,040.20	$1,040.40