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	$28.49	13.705%	$32.3946	$32.39	$32.40	$32.40
Purchase #2	$59.56	5.467%	$62.8161	$62.82	$62.80	$62.80
Purchase #3	$104.61	10.871%	$115.9822	$115.98	$116.00	$116.00
Purchase #4	$243.83	10.528%	$269.5004	$269.50	$269.50	$269.50
Purchase #5	$17.56	10.850%	$19.4653	$19.47	$19.45	$19.50
Purchase #6	$11.85	10.185%	$13.0569	$13.06	$13.05	$13.10
Purchase #7	$119.78	12.341%	$134.562	$134.56	$134.55	$134.60
7 purchase totals =	$585.68		$647.7775	$647.78	$647.75	$647.90