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	$233.55	3.561%	$241.8667	$241.87	$241.85	$241.90
Purchase #2	$112.78	12.556%	$126.9407	$126.94	$126.95	$126.90
Purchase #3	$44.80	5.493%	$47.2609	$47.26	$47.25	$47.30
Purchase #4	$138.88	3.159%	$143.2672	$143.27	$143.25	$143.30
Purchase #5	$66.61	7.266%	$71.4499	$71.45	$71.45	$71.40
Purchase #6	$164.59	4.820%	$172.5232	$172.52	$172.50	$172.50
Purchase #7	$103.28	11.465%	$115.1211	$115.12	$115.10	$115.10
7 purchase totals =	$864.49		$918.4297	$918.43	$918.35	$918.40