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	$24.38	13.715%	$27.7237	$27.72	$27.70	$27.70
Purchase #2	$70.69	11.467%	$78.796	$78.80	$78.80	$78.80
Purchase #3	$137.39	5.644%	$145.1443	$145.14	$145.15	$145.10
Purchase #4	$132.27	8.725%	$143.8106	$143.81	$143.80	$143.80
Purchase #5	$38.39	13.834%	$43.7009	$43.70	$43.70	$43.70
Purchase #6	$238.83	8.332%	$258.7293	$258.73	$258.75	$258.70
Purchase #7	$102.62	3.690%	$106.4067	$106.41	$106.40	$106.40
7 purchase totals =	$744.57		$804.3115	$804.31	$804.30	$804.20