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	$225.41	13.355%	$255.5135	$255.51	$255.50	$255.50
Purchase #2	$57.38	8.118%	$62.0381	$62.04	$62.05	$62.00
Purchase #3	$179.68	11.778%	$200.8427	$200.84	$200.85	$200.80
Purchase #4	$35.85	10.520%	$39.6214	$39.62	$39.60	$39.60
Purchase #5	$143.33	5.338%	$150.981	$150.98	$151.00	$151.00
Purchase #6	$98.77	3.552%	$102.2783	$102.28	$102.30	$102.30
Purchase #7	$48.90	6.619%	$52.1367	$52.14	$52.15	$52.10
7 purchase totals =	$789.32		$863.4117	$863.41	$863.45	$863.30