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	$97.89	9.585%	$107.2728	$107.27	$107.25	$107.30
Purchase #2	$33.33	3.852%	$34.6139	$34.61	$34.60	$34.60
Purchase #3	$65.36	5.352%	$68.8581	$68.86	$68.85	$68.90
Purchase #4	$135.68	8.641%	$147.4041	$147.40	$147.40	$147.40
Purchase #5	$76.43	3.248%	$78.9124	$78.91	$78.90	$78.90
Purchase #6	$82.32	10.310%	$90.8072	$90.81	$90.80	$90.80
Purchase #7	$18.40	13.291%	$20.8455	$20.85	$20.85	$20.80
7 purchase totals =	$509.41		$548.7140	$548.71	$548.65	$548.70