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	$65.63	10.144%	$72.2875	$72.29	$72.30	$72.30
Purchase #2	$240.25	11.749%	$268.477	$268.48	$268.50	$268.50
Purchase #3	$20.99	12.470%	$23.6075	$23.61	$23.60	$23.60
Purchase #4	$138.98	8.105%	$150.2443	$150.24	$150.25	$150.20
Purchase #5	$43.32	9.544%	$47.4545	$47.45	$47.45	$47.50
Purchase #6	$148.72	8.241%	$160.976	$160.98	$161.00	$161.00
Purchase #7	$247.70	13.201%	$280.3989	$280.40	$280.40	$280.40
7 purchase totals =	$905.59		$1,003.4457	$1,003.45	$1,003.50	$1,003.50