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	$29.25	9.306%	$31.972	$31.97	$31.95	$32.00
Purchase #2	$99.77	13.137%	$112.8768	$112.88	$112.90	$112.90
Purchase #3	$112.90	10.354%	$124.5897	$124.59	$124.60	$124.60
Purchase #4	$59.72	11.614%	$66.6559	$66.66	$66.65	$66.70
Purchase #5	$101.92	11.866%	$114.0138	$114.01	$114.00	$114.00
Purchase #6	$34.37	12.590%	$38.6972	$38.70	$38.70	$38.70
Purchase #7	$92.65	8.694%	$100.705	$100.71	$100.70	$100.70
7 purchase totals =	$530.58		$589.5104	$589.52	$589.50	$589.60