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	$233.30	8.823%	$253.8841	$253.88	$253.90	$253.90
Purchase #2	$108.45	13.807%	$123.4237	$123.42	$123.40	$123.40
Purchase #3	$159.42	10.771%	$176.5911	$176.59	$176.60	$176.60
Purchase #4	$41.64	5.204%	$43.8069	$43.81	$43.80	$43.80
Purchase #5	$75.25	9.468%	$82.3747	$82.37	$82.35	$82.40
Purchase #6	$91.84	9.188%	$100.2783	$100.28	$100.30	$100.30
Purchase #7	$126.29	8.348%	$136.8327	$136.83	$136.85	$136.80
7 purchase totals =	$836.19		$917.1915	$917.18	$917.20	$917.20