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	$239.90	4.262%	$250.1245	$250.12	$250.10	$250.10
Purchase #2	$173.43	8.700%	$188.5184	$188.52	$188.50	$188.50
Purchase #3	$119.52	11.673%	$133.4716	$133.47	$133.45	$133.50
Purchase #4	$62.27	13.622%	$70.7524	$70.75	$70.75	$70.80
Purchase #5	$208.78	10.680%	$231.0777	$231.08	$231.10	$231.10
Purchase #6	$134.86	3.786%	$139.9658	$139.97	$139.95	$140.00
Purchase #7	$189.77	9.778%	$208.3257	$208.33	$208.35	$208.30
7 purchase totals =	$1,128.53		$1,222.2361	$1,222.24	$1,222.20	$1,222.30