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	$20.25	10.600%	$22.3965	$22.40	$22.40	$22.40
Purchase #2	$189.31	10.142%	$208.5098	$208.51	$208.50	$208.50
Purchase #3	$33.92	12.826%	$38.2706	$38.27	$38.25	$38.30
Purchase #4	$59.84	11.269%	$66.5834	$66.58	$66.60	$66.60
Purchase #5	$68.72	5.802%	$72.7071	$72.71	$72.70	$72.70
Purchase #6	$5.44	11.464%	$6.0636	$6.06	$6.05	$6.10
Purchase #7	$241.67	10.454%	$266.9342	$266.93	$266.95	$266.90
7 purchase totals =	$619.15		$681.4652	$681.46	$681.45	$681.50