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	$86.47	4.725%	$90.5557	$90.56	$90.55	$90.60
Purchase #2	$178.74	3.477%	$184.9548	$184.95	$184.95	$185.00
Purchase #3	$112.41	13.380%	$127.4505	$127.45	$127.45	$127.50
Purchase #4	$246.71	6.323%	$262.3095	$262.31	$262.30	$262.30
Purchase #5	$47.47	8.320%	$51.4195	$51.42	$51.40	$51.40
Purchase #6	$37.64	6.798%	$40.1988	$40.20	$40.20	$40.20
Purchase #7	$47.87	5.511%	$50.5081	$50.51	$50.50	$50.50
7 purchase totals =	$757.31		$807.3969	$807.40	$807.35	$807.50