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	$43.43	5.187%	$45.6827	$45.68	$45.70	$45.70
Purchase #2	$103.55	10.637%	$114.5646	$114.56	$114.55	$114.60
Purchase #3	$40.30	8.509%	$43.7291	$43.73	$43.75	$43.70
Purchase #4	$52.86	13.206%	$59.8407	$59.84	$59.85	$59.80
Purchase #5	$224.82	7.231%	$241.0767	$241.08	$241.10	$241.10
Purchase #6	$100.66	5.309%	$106.004	$106.00	$106.00	$106.00
Purchase #7	$41.78	4.525%	$43.6705	$43.67	$43.65	$43.70
7 purchase totals =	$607.40		$654.5683	$654.56	$654.60	$654.60