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	$102.76	8.432%	$111.4247	$111.42	$111.40	$111.40
Purchase #2	$32.73	6.380%	$34.8182	$34.82	$34.80	$34.80
Purchase #3	$80.47	11.191%	$89.4754	$89.48	$89.50	$89.50
Purchase #4	$174.68	4.869%	$183.1852	$183.19	$183.20	$183.20
Purchase #5	$5.38	3.706%	$5.5794	$5.58	$5.60	$5.60
Purchase #6	$137.49	11.437%	$153.2147	$153.21	$153.20	$153.20
Purchase #7	$105.94	12.273%	$118.942	$118.94	$118.95	$118.90
7 purchase totals =	$639.45		$696.6396	$696.64	$696.65	$696.60