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	$29.53	10.455%	$32.6174	$32.62	$32.60	$32.60
Purchase #2	$153.27	12.130%	$171.8617	$171.86	$171.85	$171.90
Purchase #3	$208.46	10.577%	$230.5088	$230.51	$230.50	$230.50
Purchase #4	$131.30	9.729%	$144.0742	$144.07	$144.05	$144.10
Purchase #5	$143.38	3.299%	$148.1101	$148.11	$148.10	$148.10
Purchase #6	$141.28	10.492%	$156.1031	$156.10	$156.10	$156.10
Purchase #7	$233.78	9.370%	$255.6852	$255.69	$255.70	$255.70
7 purchase totals =	$1,041.00		$1,138.9605	$1,138.96	$1,138.90	$1,139.00