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	$145.64	8.824%	$158.4913	$158.49	$158.50	$158.50
Purchase #2	$208.26	11.689%	$232.6035	$232.60	$232.60	$232.60
Purchase #3	$196.83	5.841%	$208.3268	$208.33	$208.35	$208.30
Purchase #4	$239.58	4.202%	$249.6472	$249.65	$249.65	$249.60
Purchase #5	$171.38	13.383%	$194.3158	$194.32	$194.30	$194.30
Purchase #6	$51.90	9.709%	$56.939	$56.94	$56.95	$56.90
Purchase #7	$68.37	4.606%	$71.5191	$71.52	$71.50	$71.50
7 purchase totals =	$1,081.96		$1,171.8427	$1,171.85	$1,171.85	$1,171.70