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	$226.43	9.742%	$248.4888	$248.49	$248.50	$248.50
Purchase #2	$69.29	6.147%	$73.5493	$73.55	$73.55	$73.50
Purchase #3	$54.54	8.428%	$59.1366	$59.14	$59.15	$59.10
Purchase #4	$106.83	12.406%	$120.0833	$120.08	$120.10	$120.10
Purchase #5	$9.88	13.772%	$11.2407	$11.24	$11.25	$11.20
Purchase #6	$116.66	12.695%	$131.47	$131.47	$131.45	$131.50
Purchase #7	$40.54	5.283%	$42.6817	$42.68	$42.70	$42.70
7 purchase totals =	$624.17		$686.6504	$686.65	$686.70	$686.60