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	$19.27	12.158%	$21.6128	$21.61	$21.60	$21.60
Purchase #2	$140.95	3.384%	$145.7197	$145.72	$145.70	$145.70
Purchase #3	$61.54	7.849%	$66.3703	$66.37	$66.35	$66.40
Purchase #4	$226.66	12.407%	$254.7817	$254.78	$254.80	$254.80
Purchase #5	$48.59	9.791%	$53.3474	$53.35	$53.35	$53.30
Purchase #6	$35.25	13.360%	$39.9594	$39.96	$39.95	$40.00
Purchase #7	$36.43	11.342%	$40.5619	$40.56	$40.55	$40.60
7 purchase totals =	$568.69		$622.3532	$622.35	$622.30	$622.40