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	$48.92	4.745%	$51.2413	$51.24	$51.25	$51.20
Purchase #2	$53.94	11.792%	$60.3006	$60.30	$60.30	$60.30
Purchase #3	$42.67	10.828%	$47.2903	$47.29	$47.30	$47.30
Purchase #4	$53.64	11.760%	$59.9481	$59.95	$59.95	$59.90
Purchase #5	$114.47	3.491%	$118.4661	$118.47	$118.45	$118.50
Purchase #6	$100.77	11.690%	$112.55	$112.55	$112.55	$112.60
Purchase #7	$48.40	10.696%	$53.5769	$53.58	$53.60	$53.60
7 purchase totals =	$462.81		$503.3733	$503.38	$503.40	$503.40