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	$51.46	5.427%	$54.2527	$54.25	$54.25	$54.30
Purchase #2	$147.69	6.811%	$157.7492	$157.75	$157.75	$157.70
Purchase #3	$43.69	8.713%	$47.4967	$47.50	$47.50	$47.50
Purchase #4	$176.58	4.552%	$184.6179	$184.62	$184.60	$184.60
Purchase #5	$53.88	3.136%	$55.5697	$55.57	$55.55	$55.60
Purchase #6	$37.52	6.827%	$40.0815	$40.08	$40.10	$40.10
Purchase #7	$100.29	10.792%	$111.1133	$111.11	$111.10	$111.10
7 purchase totals =	$611.11		$650.8810	$650.88	$650.85	$650.90