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	$232.67	9.800%	$255.4717	$255.47	$255.45	$255.50
Purchase #2	$82.25	8.573%	$89.3013	$89.30	$89.30	$89.30
Purchase #3	$115.69	13.689%	$131.5268	$131.53	$131.55	$131.50
Purchase #4	$50.60	4.232%	$52.7414	$52.74	$52.75	$52.70
Purchase #5	$164.32	8.572%	$178.4055	$178.41	$178.40	$178.40
Purchase #6	$71.44	11.660%	$79.7699	$79.77	$79.75	$79.80
Purchase #7	$38.65	8.117%	$41.7872	$41.79	$41.80	$41.80
7 purchase totals =	$755.62		$829.0038	$829.01	$829.00	$829.00