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	$38.34	3.440%	$39.6589	$39.66	$39.65	$39.70
Purchase #2	$231.99	10.152%	$255.5416	$255.54	$255.55	$255.50
Purchase #3	$59.35	13.443%	$67.3284	$67.33	$67.35	$67.30
Purchase #4	$93.58	12.524%	$105.3	$105.30	$105.30	$105.30
Purchase #5	$193.25	8.720%	$210.1014	$210.10	$210.10	$210.10
Purchase #6	$85.77	12.609%	$96.5847	$96.58	$96.60	$96.60
Purchase #7	$175.95	4.259%	$183.4437	$183.44	$183.45	$183.40
7 purchase totals =	$878.23		$957.9587	$957.95	$958.00	$957.90