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	$77.35	4.792%	$81.0566	$81.06	$81.05	$81.10
Purchase #2	$46.74	13.183%	$52.9017	$52.90	$52.90	$52.90
Purchase #3	$137.43	5.372%	$144.8127	$144.81	$144.80	$144.80
Purchase #4	$42.49	6.513%	$45.2574	$45.26	$45.25	$45.30
Purchase #5	$77.59	10.298%	$85.5802	$85.58	$85.60	$85.60
Purchase #6	$116.69	6.170%	$123.8898	$123.89	$123.90	$123.90
Purchase #7	$76.93	6.810%	$82.1689	$82.17	$82.15	$82.20
7 purchase totals =	$575.22		$615.6673	$615.67	$615.65	$615.80