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	$46.82	10.781%	$51.8677	$51.87	$51.85	$51.90
Purchase #2	$238.52	13.124%	$269.8234	$269.82	$269.80	$269.80
Purchase #3	$77.60	7.285%	$83.2532	$83.25	$83.25	$83.30
Purchase #4	$211.50	9.613%	$231.8315	$231.83	$231.85	$231.80
Purchase #5	$77.96	4.181%	$81.2195	$81.22	$81.20	$81.20
Purchase #6	$41.55	5.124%	$43.679	$43.68	$43.70	$43.70
Purchase #7	$148.90	3.285%	$153.7914	$153.79	$153.80	$153.80
7 purchase totals =	$842.85		$915.4657	$915.46	$915.45	$915.50