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	$28.30	12.534%	$31.8471	$31.85	$31.85	$31.80
Purchase #2	$158.59	13.815%	$180.4992	$180.50	$180.50	$180.50
Purchase #3	$66.27	8.446%	$71.8672	$71.87	$71.85	$71.90
Purchase #4	$144.86	7.318%	$155.4609	$155.46	$155.45	$155.50
Purchase #5	$223.27	4.743%	$233.8597	$233.86	$233.85	$233.90
Purchase #6	$48.94	10.860%	$54.2549	$54.25	$54.25	$54.30
Purchase #7	$127.34	4.235%	$132.7328	$132.73	$132.75	$132.70
7 purchase totals =	$797.57		$860.5218	$860.52	$860.50	$860.60