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	$50.78	11.358%	$56.5476	$56.55	$56.55	$56.50
Purchase #2	$22.52	9.299%	$24.6141	$24.61	$24.60	$24.60
Purchase #3	$115.31	10.344%	$127.2377	$127.24	$127.25	$127.20
Purchase #4	$184.35	3.328%	$190.4852	$190.49	$190.50	$190.50
Purchase #5	$81.45	8.108%	$88.054	$88.05	$88.05	$88.10
Purchase #6	$186.81	9.143%	$203.89	$203.89	$203.90	$203.90
Purchase #7	$84.79	12.796%	$95.6397	$95.64	$95.65	$95.60
7 purchase totals =	$726.01		$786.4683	$786.47	$786.50	$786.40