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	$30.52	10.118%	$33.608	$33.61	$33.60	$33.60
Purchase #2	$165.78	4.466%	$173.1837	$173.18	$173.20	$173.20
Purchase #3	$194.93	5.352%	$205.3627	$205.36	$205.35	$205.40
Purchase #4	$72.94	10.509%	$80.6053	$80.61	$80.60	$80.60
Purchase #5	$184.64	6.663%	$196.9426	$196.94	$196.95	$196.90
Purchase #6	$168.34	13.452%	$190.9851	$190.99	$191.00	$191.00
Purchase #7	$248.56	4.153%	$258.8827	$258.88	$258.90	$258.90
7 purchase totals =	$1,065.71		$1,139.5701	$1,139.57	$1,139.60	$1,139.60