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	$240.52	7.447%	$258.4315	$258.43	$258.45	$258.40
Purchase #2	$139.39	9.109%	$152.087	$152.09	$152.10	$152.10
Purchase #3	$94.73	5.831%	$100.2537	$100.25	$100.25	$100.30
Purchase #4	$183.82	4.275%	$191.6783	$191.68	$191.70	$191.70
Purchase #5	$94.68	4.160%	$98.6187	$98.62	$98.60	$98.60
Purchase #6	$110.60	6.716%	$118.0279	$118.03	$118.05	$118.00
Purchase #7	$88.76	9.809%	$97.4665	$97.47	$97.45	$97.50
7 purchase totals =	$952.50		$1,016.5636	$1,016.57	$1,016.60	$1,016.60