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	$170.87	8.524%	$185.435	$185.44	$185.45	$185.40
Purchase #2	$84.44	3.627%	$87.5026	$87.50	$87.50	$87.50
Purchase #3	$107.87	3.666%	$111.8245	$111.82	$111.80	$111.80
Purchase #4	$74.25	10.547%	$82.0811	$82.08	$82.10	$82.10
Purchase #5	$66.94	5.764%	$70.7984	$70.80	$70.80	$70.80
Purchase #6	$31.89	4.719%	$33.3949	$33.39	$33.40	$33.40
Purchase #7	$62.48	5.603%	$65.9808	$65.98	$66.00	$66.00
7 purchase totals =	$598.74		$637.0173	$637.01	$637.05	$637.00