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	$53.61	9.601%	$58.7571	$58.76	$58.75	$58.80
Purchase #2	$220.66	3.152%	$227.6152	$227.62	$227.60	$227.60
Purchase #3	$217.59	10.600%	$240.6545	$240.65	$240.65	$240.70
Purchase #4	$108.25	5.792%	$114.5198	$114.52	$114.50	$114.50
Purchase #5	$38.75	3.575%	$40.1353	$40.14	$40.15	$40.10
Purchase #6	$58.72	10.835%	$65.0823	$65.08	$65.10	$65.10
Purchase #7	$28.43	3.600%	$29.4535	$29.45	$29.45	$29.50
7 purchase totals =	$726.01		$776.2177	$776.22	$776.20	$776.30