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	$159.70	11.742%	$178.452	$178.45	$178.45	$178.50
Purchase #2	$92.30	9.289%	$100.8737	$100.87	$100.85	$100.90
Purchase #3	$170.95	11.778%	$191.0845	$191.08	$191.10	$191.10
Purchase #4	$132.69	7.343%	$142.4334	$142.43	$142.45	$142.40
Purchase #5	$10.48	8.505%	$11.3713	$11.37	$11.35	$11.40
Purchase #6	$104.32	11.856%	$116.6882	$116.69	$116.70	$116.70
Purchase #7	$225.57	7.755%	$243.063	$243.06	$243.05	$243.10
7 purchase totals =	$896.01		$983.9661	$983.95	$983.95	$984.10