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	$52.25	7.617%	$56.2299	$56.23	$56.25	$56.20
Purchase #2	$191.95	3.625%	$198.9082	$198.91	$198.90	$198.90
Purchase #3	$207.42	11.767%	$231.8271	$231.83	$231.85	$231.80
Purchase #4	$238.93	4.396%	$249.4334	$249.43	$249.45	$249.40
Purchase #5	$80.30	7.562%	$86.3723	$86.37	$86.35	$86.40
Purchase #6	$123.87	13.830%	$141.0012	$141.00	$141.00	$141.00
Purchase #7	$102.37	9.314%	$111.9047	$111.90	$111.90	$111.90
7 purchase totals =	$997.09		$1,075.6768	$1,075.67	$1,075.70	$1,075.60