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	$43.69	10.859%	$48.4343	$48.43	$48.45	$48.40
Purchase #2	$56.50	7.269%	$60.607	$60.61	$60.60	$60.60
Purchase #3	$73.72	8.138%	$79.7193	$79.72	$79.70	$79.70
Purchase #4	$76.41	7.373%	$82.0437	$82.04	$82.05	$82.00
Purchase #5	$41.51	5.587%	$43.8292	$43.83	$43.85	$43.80
Purchase #6	$129.56	9.682%	$142.104	$142.10	$142.10	$142.10
Purchase #7	$176.43	7.833%	$190.2498	$190.25	$190.25	$190.20
7 purchase totals =	$597.82		$646.9873	$646.98	$647.00	$646.80