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	$53.36	5.450%	$56.2681	$56.27	$56.25	$56.30
Purchase #2	$53.51	3.286%	$55.2683	$55.27	$55.25	$55.30
Purchase #3	$218.47	3.652%	$226.4485	$226.45	$226.45	$226.40
Purchase #4	$197.67	9.126%	$215.7094	$215.71	$215.70	$215.70
Purchase #5	$117.79	8.599%	$127.9188	$127.92	$127.90	$127.90
Purchase #6	$39.72	4.596%	$41.5455	$41.55	$41.55	$41.50
Purchase #7	$29.59	13.295%	$33.524	$33.52	$33.50	$33.50
7 purchase totals =	$710.11		$756.6826	$756.69	$756.60	$756.60