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	$24.36	4.869%	$25.5461	$25.55	$25.55	$25.50
Purchase #2	$122.69	13.619%	$139.3992	$139.40	$139.40	$139.40
Purchase #3	$131.60	8.524%	$142.8176	$142.82	$142.80	$142.80
Purchase #4	$41.66	7.308%	$44.7045	$44.70	$44.70	$44.70
Purchase #5	$60.31	3.333%	$62.3201	$62.32	$62.30	$62.30
Purchase #6	$107.69	3.694%	$111.6681	$111.67	$111.65	$111.70
Purchase #7	$29.30	9.326%	$32.0325	$32.03	$32.05	$32.00
7 purchase totals =	$517.61		$558.4881	$558.49	$558.45	$558.40