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	$43.29	13.588%	$49.1722	$49.17	$49.15	$49.20
Purchase #2	$54.71	3.481%	$56.6145	$56.61	$56.60	$56.60
Purchase #3	$31.85	3.225%	$32.8772	$32.88	$32.90	$32.90
Purchase #4	$111.89	7.854%	$120.6778	$120.68	$120.70	$120.70
Purchase #5	$124.48	12.570%	$140.1271	$140.13	$140.15	$140.10
Purchase #6	$98.85	7.228%	$105.9949	$105.99	$106.00	$106.00
Purchase #7	$122.45	9.314%	$133.855	$133.86	$133.85	$133.90
7 purchase totals =	$587.52		$639.3187	$639.32	$639.35	$639.40