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	$235.98	8.177%	$255.2761	$255.28	$255.30	$255.30
Purchase #2	$231.84	6.731%	$247.4452	$247.45	$247.45	$247.40
Purchase #3	$99.30	12.693%	$111.9041	$111.90	$111.90	$111.90
Purchase #4	$195.81	10.277%	$215.9334	$215.93	$215.95	$215.90
Purchase #5	$158.29	8.615%	$171.9267	$171.93	$171.95	$171.90
Purchase #6	$211.55	13.652%	$240.4308	$240.43	$240.45	$240.40
Purchase #7	$21.70	11.665%	$24.2313	$24.23	$24.25	$24.20
7 purchase totals =	$1,154.47		$1,267.1476	$1,267.15	$1,267.25	$1,267.00