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	$157.68	13.421%	$178.8422	$178.84	$178.85	$178.80
Purchase #2	$220.67	3.454%	$228.2919	$228.29	$228.30	$228.30
Purchase #3	$49.32	4.457%	$51.5182	$51.52	$51.50	$51.50
Purchase #4	$43.74	12.732%	$49.309	$49.31	$49.30	$49.30
Purchase #5	$97.48	7.482%	$104.7735	$104.77	$104.75	$104.80
Purchase #6	$76.48	5.193%	$80.4516	$80.45	$80.45	$80.50
Purchase #7	$101.39	10.295%	$111.8281	$111.83	$111.85	$111.80
7 purchase totals =	$746.76		$805.0145	$805.01	$805.00	$805.00