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	$230.61	12.802%	$260.1327	$260.13	$260.15	$260.10
Purchase #2	$139.86	10.466%	$154.4977	$154.50	$154.50	$154.50
Purchase #3	$84.67	5.582%	$89.3963	$89.40	$89.40	$89.40
Purchase #4	$232.86	12.566%	$262.1212	$262.12	$262.10	$262.10
Purchase #5	$205.32	10.426%	$226.7267	$226.73	$226.75	$226.70
Purchase #6	$12.67	6.528%	$13.4971	$13.50	$13.50	$13.50
Purchase #7	$158.83	8.191%	$171.8398	$171.84	$171.85	$171.80
7 purchase totals =	$1,064.82		$1,178.2115	$1,178.22	$1,178.25	$1,178.10