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	$33.85	9.246%	$36.9798	$36.98	$37.00	$37.00
Purchase #2	$229.44	4.859%	$240.5885	$240.59	$240.60	$240.60
Purchase #3	$15.95	7.651%	$17.1703	$17.17	$17.15	$17.20
Purchase #4	$133.49	9.714%	$146.4572	$146.46	$146.45	$146.50
Purchase #5	$35.25	7.376%	$37.85	$37.85	$37.85	$37.90
Purchase #6	$34.49	12.411%	$38.7706	$38.77	$38.75	$38.80
Purchase #7	$60.40	7.456%	$64.9034	$64.90	$64.90	$64.90
7 purchase totals =	$542.87		$582.7198	$582.72	$582.70	$582.90