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	$238.52	12.365%	$268.013	$268.01	$268.00	$268.00
Purchase #2	$48.55	6.558%	$51.7339	$51.73	$51.75	$51.70
Purchase #3	$91.78	10.826%	$101.7161	$101.72	$101.70	$101.70
Purchase #4	$10.96	4.824%	$11.4887	$11.49	$11.50	$11.50
Purchase #5	$32.61	9.131%	$35.5876	$35.59	$35.60	$35.60
Purchase #6	$136.86	4.424%	$142.9147	$142.91	$142.90	$142.90
Purchase #7	$43.36	8.724%	$47.1427	$47.14	$47.15	$47.10
7 purchase totals =	$602.64		$658.5967	$658.59	$658.60	$658.50