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	$226.26	13.305%	$256.3639	$256.36	$256.35	$256.40
Purchase #2	$200.43	13.545%	$227.5782	$227.58	$227.60	$227.60
Purchase #3	$36.35	11.838%	$40.6531	$40.65	$40.65	$40.70
Purchase #4	$31.80	6.306%	$33.8053	$33.81	$33.80	$33.80
Purchase #5	$10.40	3.619%	$10.7764	$10.78	$10.80	$10.80
Purchase #6	$147.44	4.162%	$153.5765	$153.58	$153.60	$153.60
Purchase #7	$39.32	9.534%	$43.0688	$43.07	$43.05	$43.10
7 purchase totals =	$692.00		$765.8222	$765.83	$765.85	$766.00