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	$52.51	12.545%	$59.0974	$59.10	$59.10	$59.10
Purchase #2	$112.83	9.646%	$123.7136	$123.71	$123.70	$123.70
Purchase #3	$177.82	5.453%	$187.5165	$187.52	$187.50	$187.50
Purchase #4	$112.90	12.631%	$127.1604	$127.16	$127.15	$127.20
Purchase #5	$201.68	8.457%	$218.7361	$218.74	$218.75	$218.70
Purchase #6	$126.46	10.103%	$139.2363	$139.24	$139.25	$139.20
Purchase #7	$37.75	4.493%	$39.4461	$39.45	$39.45	$39.40
7 purchase totals =	$821.95		$894.9064	$894.92	$894.90	$894.80