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	$245.44	4.553%	$256.6149	$256.61	$256.60	$256.60
Purchase #2	$141.41	12.285%	$158.7822	$158.78	$158.80	$158.80
Purchase #3	$237.86	6.478%	$253.2686	$253.27	$253.25	$253.30
Purchase #4	$38.46	7.447%	$41.3241	$41.32	$41.30	$41.30
Purchase #5	$214.38	6.729%	$228.8056	$228.81	$228.80	$228.80
Purchase #6	$213.68	4.778%	$223.8896	$223.89	$223.90	$223.90
Purchase #7	$88.25	7.466%	$94.8387	$94.84	$94.85	$94.80
7 purchase totals =	$1,179.48		$1,257.5237	$1,257.52	$1,257.50	$1,257.50