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	$239.49	7.214%	$256.7668	$256.77	$256.75	$256.80
Purchase #2	$90.97	9.712%	$99.805	$99.81	$99.80	$99.80
Purchase #3	$187.43	3.410%	$193.8214	$193.82	$193.80	$193.80
Purchase #4	$123.98	13.871%	$141.1773	$141.18	$141.20	$141.20
Purchase #5	$60.41	5.385%	$63.6631	$63.66	$63.65	$63.70
Purchase #6	$34.83	10.454%	$38.4711	$38.47	$38.45	$38.50
Purchase #7	$83.60	3.667%	$86.6656	$86.67	$86.65	$86.70
7 purchase totals =	$820.71		$880.3703	$880.38	$880.30	$880.50