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	$240.27	8.334%	$260.2941	$260.29	$260.30	$260.30
Purchase #2	$74.71	12.248%	$83.8605	$83.86	$83.85	$83.90
Purchase #3	$171.35	11.795%	$191.5607	$191.56	$191.55	$191.60
Purchase #4	$217.45	9.588%	$238.2991	$238.30	$238.30	$238.30
Purchase #5	$142.48	7.659%	$153.3925	$153.39	$153.40	$153.40
Purchase #6	$34.66	9.669%	$38.0113	$38.01	$38.00	$38.00
Purchase #7	$139.67	13.341%	$158.3034	$158.30	$158.30	$158.30
7 purchase totals =	$1,020.59		$1,123.7216	$1,123.71	$1,123.70	$1,123.80