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	$166.25	6.209%	$176.5725	$176.57	$176.55	$176.60
Purchase #2	$122.27	13.279%	$138.5062	$138.51	$138.50	$138.50
Purchase #3	$52.83	12.161%	$59.2547	$59.25	$59.25	$59.30
Purchase #4	$146.85	12.514%	$165.2268	$165.23	$165.25	$165.20
Purchase #5	$238.46	4.514%	$249.2241	$249.22	$249.20	$249.20
Purchase #6	$78.53	10.326%	$86.639	$86.64	$86.65	$86.60
Purchase #7	$243.80	8.116%	$263.5868	$263.59	$263.60	$263.60
7 purchase totals =	$1,048.99		$1,139.0101	$1,139.01	$1,139.00	$1,139.00