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	$249.35	6.105%	$264.5728	$264.57	$264.55	$264.60
Purchase #2	$33.77	8.112%	$36.5094	$36.51	$36.50	$36.50
Purchase #3	$49.63	5.697%	$52.4574	$52.46	$52.45	$52.50
Purchase #4	$81.77	9.739%	$89.7336	$89.73	$89.75	$89.70
Purchase #5	$63.70	3.567%	$65.9722	$65.97	$65.95	$66.00
Purchase #6	$30.80	13.175%	$34.8579	$34.86	$34.85	$34.90
Purchase #7	$63.80	3.798%	$66.2231	$66.22	$66.20	$66.20
7 purchase totals =	$572.82		$610.3264	$610.32	$610.25	$610.40