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	$206.78	7.514%	$222.3174	$222.32	$222.30	$222.30
Purchase #2	$143.90	9.486%	$157.5504	$157.55	$157.55	$157.60
Purchase #3	$149.43	12.591%	$168.2447	$168.24	$168.25	$168.20
Purchase #4	$243.74	11.141%	$270.8951	$270.90	$270.90	$270.90
Purchase #5	$248.27	13.157%	$280.9349	$280.93	$280.95	$280.90
Purchase #6	$125.72	9.477%	$137.6345	$137.63	$137.65	$137.60
Purchase #7	$15.61	12.139%	$17.5049	$17.50	$17.50	$17.50
7 purchase totals =	$1,133.45		$1,255.0819	$1,255.07	$1,255.10	$1,255.00