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	$141.87	12.444%	$159.5243	$159.52	$159.50	$159.50
Purchase #2	$92.27	7.482%	$99.1736	$99.17	$99.15	$99.20
Purchase #3	$116.33	5.784%	$123.0585	$123.06	$123.05	$123.10
Purchase #4	$125.26	11.121%	$139.1902	$139.19	$139.20	$139.20
Purchase #5	$183.78	11.852%	$205.5616	$205.56	$205.55	$205.60
Purchase #6	$119.56	4.239%	$124.6281	$124.63	$124.65	$124.60
Purchase #7	$111.29	6.481%	$118.5027	$118.50	$118.50	$118.50
7 purchase totals =	$890.36		$969.6390	$969.63	$969.60	$969.70