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	$11.63	7.508%	$12.5032	$12.50	$12.50	$12.50
Purchase #2	$243.35	7.697%	$262.0806	$262.08	$262.10	$262.10
Purchase #3	$239.74	6.720%	$255.8505	$255.85	$255.85	$255.90
Purchase #4	$123.63	12.630%	$139.2445	$139.24	$139.25	$139.20
Purchase #5	$194.39	12.523%	$218.7335	$218.73	$218.75	$218.70
Purchase #6	$116.50	9.723%	$127.8273	$127.83	$127.85	$127.80
Purchase #7	$116.72	10.212%	$128.6394	$128.64	$128.65	$128.60
7 purchase totals =	$1,045.96		$1,144.8790	$1,144.87	$1,144.95	$1,144.80