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	$26.82	3.488%	$27.7555	$27.76	$27.75	$27.80
Purchase #2	$56.37	3.552%	$58.3723	$58.37	$58.35	$58.40
Purchase #3	$20.36	6.448%	$21.6728	$21.67	$21.65	$21.70
Purchase #4	$123.43	11.503%	$137.6282	$137.63	$137.65	$137.60
Purchase #5	$43.42	9.233%	$47.429	$47.43	$47.45	$47.40
Purchase #6	$42.30	3.697%	$43.8638	$43.86	$43.85	$43.90
Purchase #7	$212.85	4.571%	$222.5794	$222.58	$222.60	$222.60
7 purchase totals =	$525.55		$559.3010	$559.30	$559.30	$559.40