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	$140.71	12.491%	$158.2861	$158.29	$158.30	$158.30
Purchase #2	$38.29	12.311%	$43.0039	$43.00	$43.00	$43.00
Purchase #3	$61.76	4.437%	$64.5003	$64.50	$64.50	$64.50
Purchase #4	$139.33	12.295%	$156.4606	$156.46	$156.45	$156.50
Purchase #5	$94.81	3.666%	$98.2857	$98.29	$98.30	$98.30
Purchase #6	$18.37	8.336%	$19.9013	$19.90	$19.90	$19.90
Purchase #7	$243.25	9.409%	$266.1374	$266.14	$266.15	$266.10
7 purchase totals =	$736.52		$806.5753	$806.58	$806.60	$806.60