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	$112.94	13.323%	$127.987	$127.99	$128.00	$128.00
Purchase #2	$115.87	5.411%	$122.1397	$122.14	$122.15	$122.10
Purchase #3	$33.74	10.159%	$37.1676	$37.17	$37.15	$37.20
Purchase #4	$93.50	7.865%	$100.8538	$100.85	$100.85	$100.90
Purchase #5	$240.27	8.239%	$260.0658	$260.07	$260.05	$260.10
Purchase #6	$82.96	7.837%	$89.4616	$89.46	$89.45	$89.50
Purchase #7	$172.81	13.497%	$196.1342	$196.13	$196.15	$196.10
7 purchase totals =	$852.09		$933.8097	$933.81	$933.80	$933.90