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	$102.38	3.264%	$105.7217	$105.72	$105.70	$105.70
Purchase #2	$186.45	11.872%	$208.5853	$208.59	$208.60	$208.60
Purchase #3	$130.31	6.716%	$139.0616	$139.06	$139.05	$139.10
Purchase #4	$227.60	12.103%	$255.1464	$255.15	$255.15	$255.10
Purchase #5	$35.39	7.678%	$38.1072	$38.11	$38.10	$38.10
Purchase #6	$67.64	3.290%	$69.8654	$69.87	$69.85	$69.90
Purchase #7	$162.85	8.578%	$176.8193	$176.82	$176.80	$176.80
7 purchase totals =	$912.62		$993.3069	$993.32	$993.25	$993.30