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	$163.59	6.256%	$173.8242	$173.82	$173.80	$173.80
Purchase #2	$172.87	3.461%	$178.853	$178.85	$178.85	$178.90
Purchase #3	$85.58	4.512%	$89.4414	$89.44	$89.45	$89.40
Purchase #4	$172.30	12.745%	$194.2596	$194.26	$194.25	$194.30
Purchase #5	$133.84	5.550%	$141.2681	$141.27	$141.25	$141.30
Purchase #6	$226.34	13.509%	$256.9163	$256.92	$256.90	$256.90
Purchase #7	$175.86	11.856%	$196.71	$196.71	$196.70	$196.70
7 purchase totals =	$1,130.38		$1,231.2726	$1,231.27	$1,231.20	$1,231.30