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	$15.88	10.176%	$17.4959	$17.50	$17.50	$17.50
Purchase #2	$115.89	9.831%	$127.2831	$127.28	$127.30	$127.30
Purchase #3	$206.87	4.340%	$215.8482	$215.85	$215.85	$215.80
Purchase #4	$232.73	5.679%	$245.9467	$245.95	$245.95	$245.90
Purchase #5	$223.50	3.312%	$230.9023	$230.90	$230.90	$230.90
Purchase #6	$210.85	4.634%	$220.6208	$220.62	$220.60	$220.60
Purchase #7	$239.82	4.457%	$250.5088	$250.51	$250.50	$250.50
7 purchase totals =	$1,245.54		$1,308.6058	$1,308.61	$1,308.60	$1,308.50