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	$12.73	3.568%	$13.1842	$13.18	$13.20	$13.20
Purchase #2	$144.71	7.759%	$155.938	$155.94	$155.95	$155.90
Purchase #3	$71.86	9.132%	$78.4223	$78.42	$78.40	$78.40
Purchase #4	$47.38	8.279%	$51.3026	$51.30	$51.30	$51.30
Purchase #5	$111.75	10.493%	$123.4759	$123.48	$123.50	$123.50
Purchase #6	$126.78	12.407%	$142.5096	$142.51	$142.50	$142.50
Purchase #7	$87.80	11.239%	$97.6678	$97.67	$97.65	$97.70
7 purchase totals =	$603.01		$662.5004	$662.50	$662.50	$662.50