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	$49.86	13.263%	$56.4729	$56.47	$56.45	$56.50
Purchase #2	$212.40	5.730%	$224.5705	$224.57	$224.55	$224.60
Purchase #3	$94.38	9.364%	$103.2177	$103.22	$103.20	$103.20
Purchase #4	$108.87	10.718%	$120.5387	$120.54	$120.55	$120.50
Purchase #5	$213.32	8.510%	$231.4735	$231.47	$231.45	$231.50
Purchase #6	$13.79	4.271%	$14.379	$14.38	$14.40	$14.40
Purchase #7	$101.99	9.723%	$111.9065	$111.91	$111.90	$111.90
7 purchase totals =	$794.61		$862.5588	$862.56	$862.50	$862.60