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	$249.97	12.344%	$280.8263	$280.83	$280.85	$280.80
Purchase #2	$109.81	6.204%	$116.6226	$116.62	$116.60	$116.60
Purchase #3	$13.42	3.608%	$13.9042	$13.90	$13.90	$13.90
Purchase #4	$18.56	3.450%	$19.2003	$19.20	$19.20	$19.20
Purchase #5	$139.80	7.869%	$150.8009	$150.80	$150.80	$150.80
Purchase #6	$196.92	13.179%	$222.8721	$222.87	$222.85	$222.90
Purchase #7	$72.61	6.811%	$77.5555	$77.56	$77.55	$77.60
7 purchase totals =	$801.09		$881.7819	$881.78	$881.75	$881.80