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	$109.72	13.382%	$124.4027	$124.40	$124.40	$124.40
Purchase #2	$139.48	13.403%	$158.1745	$158.17	$158.15	$158.20
Purchase #3	$153.76	11.360%	$171.2271	$171.23	$171.25	$171.20
Purchase #4	$28.55	8.808%	$31.0647	$31.06	$31.05	$31.10
Purchase #5	$29.79	10.124%	$32.8059	$32.81	$32.80	$32.80
Purchase #6	$192.58	11.286%	$214.3146	$214.31	$214.30	$214.30
Purchase #7	$44.88	8.272%	$48.5925	$48.59	$48.60	$48.60
7 purchase totals =	$698.76		$780.5820	$780.57	$780.55	$780.60