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	$78.26	10.556%	$86.5211	$86.52	$86.50	$86.50
Purchase #2	$218.75	5.670%	$231.1531	$231.15	$231.15	$231.20
Purchase #3	$112.56	9.354%	$123.0889	$123.09	$123.10	$123.10
Purchase #4	$123.38	8.653%	$134.0561	$134.06	$134.05	$134.10
Purchase #5	$56.45	7.820%	$60.8644	$60.86	$60.85	$60.90
Purchase #6	$100.42	9.156%	$109.6145	$109.61	$109.60	$109.60
Purchase #7	$52.48	4.108%	$54.6359	$54.64	$54.65	$54.60
7 purchase totals =	$742.30		$799.9340	$799.93	$799.90	$800.00