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	$36.56	5.616%	$38.6132	$38.61	$38.60	$38.60
Purchase #2	$179.35	11.754%	$200.4308	$200.43	$200.45	$200.40
Purchase #3	$222.94	6.868%	$238.2515	$238.25	$238.25	$238.30
Purchase #4	$126.36	10.294%	$139.3675	$139.37	$139.35	$139.40
Purchase #5	$49.59	9.801%	$54.4503	$54.45	$54.45	$54.50
Purchase #6	$93.84	8.249%	$101.5809	$101.58	$101.60	$101.60
Purchase #7	$248.51	7.321%	$266.7034	$266.70	$266.70	$266.70
7 purchase totals =	$957.15		$1,039.3976	$1,039.39	$1,039.40	$1,039.50