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	$209.72	12.781%	$236.5243	$236.52	$236.50	$236.50
Purchase #2	$75.74	3.851%	$78.6567	$78.66	$78.65	$78.70
Purchase #3	$102.95	8.693%	$111.8994	$111.90	$111.90	$111.90
Purchase #4	$16.99	8.838%	$18.4916	$18.49	$18.50	$18.50
Purchase #5	$74.32	4.401%	$77.5908	$77.59	$77.60	$77.60
Purchase #6	$177.27	9.198%	$193.5753	$193.58	$193.60	$193.60
Purchase #7	$63.57	12.433%	$71.4737	$71.47	$71.45	$71.50
7 purchase totals =	$720.56		$788.2118	$788.21	$788.20	$788.30