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	$51.62	9.725%	$56.64	$56.64	$56.65	$56.60
Purchase #2	$110.49	6.633%	$117.8188	$117.82	$117.80	$117.80
Purchase #3	$189.57	3.822%	$196.8154	$196.82	$196.80	$196.80
Purchase #4	$12.73	8.231%	$13.7778	$13.78	$13.80	$13.80
Purchase #5	$16.27	5.450%	$17.1567	$17.16	$17.15	$17.20
Purchase #6	$136.85	4.597%	$143.141	$143.14	$143.15	$143.10
Purchase #7	$39.69	13.222%	$44.9378	$44.94	$44.95	$44.90
7 purchase totals =	$557.22		$590.2875	$590.30	$590.30	$590.20