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	$75.50	3.674%	$78.2739	$78.27	$78.25	$78.30
Purchase #2	$65.50	7.737%	$70.5677	$70.57	$70.55	$70.60
Purchase #3	$93.83	9.345%	$102.5984	$102.60	$102.60	$102.60
Purchase #4	$39.55	4.858%	$41.4713	$41.47	$41.45	$41.50
Purchase #5	$35.40	10.321%	$39.0536	$39.05	$39.05	$39.10
Purchase #6	$187.84	3.601%	$194.6041	$194.60	$194.60	$194.60
Purchase #7	$124.94	5.268%	$131.5218	$131.52	$131.50	$131.50
7 purchase totals =	$622.56		$658.0908	$658.08	$658.00	$658.20