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	$48.70	11.433%	$54.2679	$54.27	$54.25	$54.30
Purchase #2	$227.56	4.152%	$237.0083	$237.01	$237.00	$237.00
Purchase #3	$158.61	13.195%	$179.5386	$179.54	$179.55	$179.50
Purchase #4	$134.48	12.411%	$151.1703	$151.17	$151.15	$151.20
Purchase #5	$113.66	8.680%	$123.5257	$123.53	$123.55	$123.50
Purchase #6	$66.39	13.468%	$75.3314	$75.33	$75.35	$75.30
Purchase #7	$113.93	5.136%	$119.7814	$119.78	$119.80	$119.80
7 purchase totals =	$863.33		$940.6236	$940.63	$940.65	$940.60