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	$215.86	12.714%	$243.3044	$243.30	$243.30	$243.30
Purchase #2	$250.95	9.842%	$275.6485	$275.65	$275.65	$275.60
Purchase #3	$53.80	13.552%	$61.091	$61.09	$61.10	$61.10
Purchase #4	$12.84	3.538%	$13.2943	$13.29	$13.30	$13.30
Purchase #5	$158.84	13.705%	$180.609	$180.61	$180.60	$180.60
Purchase #6	$70.29	3.109%	$72.4753	$72.48	$72.50	$72.50
Purchase #7	$12.79	3.724%	$13.2663	$13.27	$13.25	$13.30
7 purchase totals =	$775.37		$859.6888	$859.69	$859.70	$859.70