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	$167.88	6.594%	$178.95	$178.95	$178.95	$179.00
Purchase #2	$246.64	13.577%	$280.1263	$280.13	$280.15	$280.10
Purchase #3	$47.57	13.222%	$53.8597	$53.86	$53.85	$53.90
Purchase #4	$108.40	3.169%	$111.8352	$111.84	$111.85	$111.80
Purchase #5	$214.87	12.297%	$241.2926	$241.29	$241.30	$241.30
Purchase #6	$238.93	12.127%	$267.905	$267.91	$267.90	$267.90
Purchase #7	$80.38	4.223%	$83.7744	$83.77	$83.75	$83.80
7 purchase totals =	$1,104.67		$1,217.7432	$1,217.75	$1,217.75	$1,217.80