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	$100.59	8.680%	$109.3212	$109.32	$109.30	$109.30
Purchase #2	$120.43	4.851%	$126.2721	$126.27	$126.25	$126.30
Purchase #3	$203.75	8.642%	$221.3581	$221.36	$221.35	$221.40
Purchase #4	$39.90	7.146%	$42.7513	$42.75	$42.75	$42.80
Purchase #5	$235.37	12.767%	$265.4197	$265.42	$265.40	$265.40
Purchase #6	$151.79	4.626%	$158.8118	$158.81	$158.80	$158.80
Purchase #7	$47.93	8.212%	$51.866	$51.87	$51.85	$51.90
7 purchase totals =	$899.76		$975.8002	$975.80	$975.70	$975.90