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	$240.64	6.184%	$255.5212	$255.52	$255.50	$255.50
Purchase #2	$52.67	9.381%	$57.611	$57.61	$57.60	$57.60
Purchase #3	$85.50	3.673%	$88.6404	$88.64	$88.65	$88.60
Purchase #4	$116.92	5.647%	$123.5225	$123.52	$123.50	$123.50
Purchase #5	$12.97	10.718%	$14.3601	$14.36	$14.35	$14.40
Purchase #6	$10.47	13.268%	$11.8592	$11.86	$11.85	$11.90
Purchase #7	$126.95	9.570%	$139.0991	$139.10	$139.10	$139.10
7 purchase totals =	$646.12		$690.6135	$690.61	$690.55	$690.60