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	$81.66	9.666%	$89.5533	$89.55	$89.55	$89.60
Purchase #2	$199.78	11.181%	$222.1174	$222.12	$222.10	$222.10
Purchase #3	$30.82	3.565%	$31.9187	$31.92	$31.90	$31.90
Purchase #4	$127.41	12.558%	$143.4101	$143.41	$143.40	$143.40
Purchase #5	$210.47	13.568%	$239.0266	$239.03	$239.05	$239.00
Purchase #6	$9.29	8.698%	$10.098	$10.10	$10.10	$10.10
Purchase #7	$221.70	13.589%	$251.8268	$251.83	$251.85	$251.80
7 purchase totals =	$881.13		$987.9509	$987.96	$987.95	$987.90