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	$22.39	8.494%	$24.2918	$24.29	$24.30	$24.30
Purchase #2	$184.46	6.767%	$196.9424	$196.94	$196.95	$196.90
Purchase #3	$76.50	5.395%	$80.6272	$80.63	$80.65	$80.60
Purchase #4	$155.39	5.716%	$164.2721	$164.27	$164.25	$164.30
Purchase #5	$158.60	4.758%	$166.1462	$166.15	$166.15	$166.10
Purchase #6	$156.45	10.670%	$173.1432	$173.14	$173.15	$173.10
Purchase #7	$100.54	13.848%	$114.4628	$114.46	$114.45	$114.50
7 purchase totals =	$854.33		$919.8857	$919.88	$919.90	$919.80