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	$27.30	8.421%	$29.5989	$29.60	$29.60	$29.60
Purchase #2	$216.94	13.702%	$246.6651	$246.67	$246.65	$246.70
Purchase #3	$101.98	9.356%	$111.5212	$111.52	$111.50	$111.50
Purchase #4	$248.33	5.750%	$262.609	$262.61	$262.60	$262.60
Purchase #5	$186.63	5.453%	$196.8069	$196.81	$196.80	$196.80
Purchase #6	$10.51	4.455%	$10.9782	$10.98	$11.00	$11.00
Purchase #7	$169.72	10.555%	$187.6339	$187.63	$187.65	$187.60
7 purchase totals =	$961.41		$1,045.8132	$1,045.82	$1,045.80	$1,045.80