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	$17.78	13.725%	$20.2203	$20.22	$20.20	$20.20
Purchase #2	$36.52	8.728%	$39.7075	$39.71	$39.70	$39.70
Purchase #3	$40.81	11.532%	$45.5162	$45.52	$45.50	$45.50
Purchase #4	$216.45	3.874%	$224.8353	$224.84	$224.85	$224.80
Purchase #5	$10.26	10.328%	$11.3197	$11.32	$11.30	$11.30
Purchase #6	$46.57	4.186%	$48.5194	$48.52	$48.50	$48.50
Purchase #7	$38.25	13.824%	$43.5377	$43.54	$43.55	$43.50
7 purchase totals =	$406.64		$433.6561	$433.67	$433.60	$433.50