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	$49.79	13.703%	$56.6127	$56.61	$56.60	$56.60
Purchase #2	$81.95	9.688%	$89.8893	$89.89	$89.90	$89.90
Purchase #3	$60.79	13.405%	$68.9389	$68.94	$68.95	$68.90
Purchase #4	$100.41	12.152%	$112.6118	$112.61	$112.60	$112.60
Purchase #5	$134.70	3.115%	$138.8959	$138.90	$138.90	$138.90
Purchase #6	$172.63	4.413%	$180.2482	$180.25	$180.25	$180.20
Purchase #7	$214.37	8.754%	$233.1359	$233.14	$233.15	$233.10
7 purchase totals =	$814.64		$880.3327	$880.34	$880.35	$880.20