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	$171.70	5.298%	$180.7967	$180.80	$180.80	$180.80
Purchase #2	$40.31	8.187%	$43.6102	$43.61	$43.60	$43.60
Purchase #3	$136.80	5.389%	$144.1722	$144.17	$144.15	$144.20
Purchase #4	$230.36	10.423%	$254.3704	$254.37	$254.35	$254.40
Purchase #5	$237.56	10.304%	$262.0382	$262.04	$262.05	$262.00
Purchase #6	$36.30	11.595%	$40.509	$40.51	$40.50	$40.50
Purchase #7	$122.59	7.500%	$131.7843	$131.78	$131.80	$131.80
7 purchase totals =	$975.62		$1,057.2810	$1,057.28	$1,057.25	$1,057.30