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	$198.44	8.462%	$215.232	$215.23	$215.25	$215.20
Purchase #2	$249.38	8.476%	$270.5174	$270.52	$270.50	$270.50
Purchase #3	$16.96	10.173%	$18.6853	$18.69	$18.70	$18.70
Purchase #4	$132.82	13.599%	$150.8822	$150.88	$150.90	$150.90
Purchase #5	$122.27	12.310%	$137.3214	$137.32	$137.30	$137.30
Purchase #6	$224.94	4.373%	$234.7766	$234.78	$234.80	$234.80
Purchase #7	$36.59	5.679%	$38.6679	$38.67	$38.65	$38.70
7 purchase totals =	$981.40		$1,066.0828	$1,066.09	$1,066.10	$1,066.10