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	$101.39	9.836%	$111.3627	$111.36	$111.35	$111.40
Purchase #2	$151.66	7.707%	$163.3484	$163.35	$163.35	$163.30
Purchase #3	$234.59	7.774%	$252.827	$252.83	$252.85	$252.80
Purchase #4	$40.35	5.304%	$42.4902	$42.49	$42.50	$42.50
Purchase #5	$75.53	9.819%	$82.9463	$82.95	$82.95	$82.90
Purchase #6	$42.47	12.751%	$47.8853	$47.89	$47.90	$47.90
Purchase #7	$90.57	13.247%	$102.5678	$102.57	$102.55	$102.60
7 purchase totals =	$736.56		$803.4277	$803.44	$803.45	$803.40