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	$20.45	3.532%	$21.1723	$21.17	$21.15	$21.20
Purchase #2	$196.44	13.238%	$222.4447	$222.44	$222.45	$222.40
Purchase #3	$205.76	3.215%	$212.3752	$212.38	$212.40	$212.40
Purchase #4	$89.73	13.569%	$101.9055	$101.91	$101.90	$101.90
Purchase #5	$48.65	5.280%	$51.2187	$51.22	$51.20	$51.20
Purchase #6	$43.88	10.726%	$48.5866	$48.59	$48.60	$48.60
Purchase #7	$143.53	5.824%	$151.8892	$151.89	$151.90	$151.90
7 purchase totals =	$748.44		$809.5922	$809.60	$809.60	$809.60