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	$103.82	12.602%	$116.9034	$116.90	$116.90	$116.90
Purchase #2	$143.32	6.398%	$152.4896	$152.49	$152.50	$152.50
Purchase #3	$6.95	9.222%	$7.5909	$7.59	$7.60	$7.60
Purchase #4	$90.83	7.741%	$97.8612	$97.86	$97.85	$97.90
Purchase #5	$152.59	12.726%	$172.0086	$172.01	$172.00	$172.00
Purchase #6	$171.93	4.521%	$179.703	$179.70	$179.70	$179.70
Purchase #7	$51.59	3.313%	$53.2992	$53.30	$53.30	$53.30
7 purchase totals =	$721.03		$779.8559	$779.85	$779.85	$779.90