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	$120.65	9.827%	$132.5063	$132.51	$132.50	$132.50
Purchase #2	$83.77	12.280%	$94.057	$94.06	$94.05	$94.10
Purchase #3	$100.38	5.513%	$105.9139	$105.91	$105.90	$105.90
Purchase #4	$33.47	10.221%	$36.891	$36.89	$36.90	$36.90
Purchase #5	$187.51	11.413%	$208.9105	$208.91	$208.90	$208.90
Purchase #6	$214.47	6.490%	$228.3891	$228.39	$228.40	$228.40
Purchase #7	$111.79	4.411%	$116.7211	$116.72	$116.70	$116.70
7 purchase totals =	$852.04		$923.3889	$923.39	$923.35	$923.40