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	$132.32	9.111%	$144.3757	$144.38	$144.40	$144.40
Purchase #2	$169.80	11.697%	$189.6615	$189.66	$189.65	$189.70
Purchase #3	$25.78	8.491%	$27.969	$27.97	$27.95	$28.00
Purchase #4	$137.98	5.403%	$145.4351	$145.44	$145.45	$145.40
Purchase #5	$158.40	3.863%	$164.519	$164.52	$164.50	$164.50
Purchase #6	$205.73	9.103%	$224.4576	$224.46	$224.45	$224.50
Purchase #7	$14.32	8.410%	$15.5243	$15.52	$15.50	$15.50
7 purchase totals =	$844.33		$911.9422	$911.95	$911.90	$912.00