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	$79.77	4.619%	$83.4546	$83.45	$83.45	$83.50
Purchase #2	$7.73	13.258%	$8.7548	$8.75	$8.75	$8.80
Purchase #3	$81.77	10.390%	$90.2659	$90.27	$90.25	$90.30
Purchase #4	$155.86	10.737%	$172.5947	$172.59	$172.60	$172.60
Purchase #5	$241.52	3.397%	$249.7244	$249.72	$249.70	$249.70
Purchase #6	$186.25	12.667%	$209.8423	$209.84	$209.85	$209.80
Purchase #7	$33.67	9.719%	$36.9424	$36.94	$36.95	$36.90
7 purchase totals =	$786.57		$851.5791	$851.56	$851.55	$851.60