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	$118.55	13.455%	$134.5009	$134.50	$134.50	$134.50
Purchase #2	$38.58	3.715%	$40.0132	$40.01	$40.00	$40.00
Purchase #3	$61.63	6.435%	$65.5959	$65.60	$65.60	$65.60
Purchase #4	$46.27	9.354%	$50.5981	$50.60	$50.60	$50.60
Purchase #5	$5.56	12.535%	$6.2569	$6.26	$6.25	$6.30
Purchase #6	$227.52	4.594%	$237.9723	$237.97	$237.95	$238.00
Purchase #7	$50.43	12.839%	$56.9047	$56.90	$56.90	$56.90
7 purchase totals =	$548.54		$591.8420	$591.84	$591.80	$591.90