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	$9.68	12.314%	$10.872	$10.87	$10.85	$10.90
Purchase #2	$143.83	4.524%	$150.3369	$150.34	$150.35	$150.30
Purchase #3	$143.42	10.706%	$158.7745	$158.77	$158.75	$158.80
Purchase #4	$35.94	13.431%	$40.7671	$40.77	$40.75	$40.80
Purchase #5	$57.87	8.551%	$62.8185	$62.82	$62.80	$62.80
Purchase #6	$222.85	9.535%	$244.0987	$244.10	$244.10	$244.10
Purchase #7	$11.94	11.467%	$13.3092	$13.31	$13.30	$13.30
7 purchase totals =	$625.53		$680.9769	$680.98	$680.90	$681.00