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	$10.77	8.870%	$11.7253	$11.73	$11.75	$11.70
Purchase #2	$32.82	7.870%	$35.4029	$35.40	$35.40	$35.40
Purchase #3	$97.45	5.328%	$102.6421	$102.64	$102.65	$102.60
Purchase #4	$111.73	6.491%	$118.9824	$118.98	$119.00	$119.00
Purchase #5	$28.72	13.490%	$32.5943	$32.59	$32.60	$32.60
Purchase #6	$178.97	4.455%	$186.9431	$186.94	$186.95	$186.90
Purchase #7	$9.56	7.232%	$10.2514	$10.25	$10.25	$10.30
7 purchase totals =	$470.02		$498.5415	$498.53	$498.60	$498.50