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	$200.57	8.843%	$218.3064	$218.31	$218.30	$218.30
Purchase #2	$62.92	6.251%	$66.8531	$66.85	$66.85	$66.90
Purchase #3	$233.86	13.389%	$265.1715	$265.17	$265.15	$265.20
Purchase #4	$41.27	5.628%	$43.5927	$43.59	$43.60	$43.60
Purchase #5	$140.33	3.689%	$145.5068	$145.51	$145.50	$145.50
Purchase #6	$35.25	9.661%	$38.6555	$38.66	$38.65	$38.70
Purchase #7	$194.38	7.606%	$209.1645	$209.16	$209.15	$209.20
7 purchase totals =	$908.58		$987.2505	$987.25	$987.20	$987.40