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	$52.52	3.274%	$54.2395	$54.24	$54.25	$54.20
Purchase #2	$171.58	12.237%	$192.5762	$192.58	$192.60	$192.60
Purchase #3	$172.90	3.149%	$178.3446	$178.34	$178.35	$178.30
Purchase #4	$176.47	6.409%	$187.78	$187.78	$187.80	$187.80
Purchase #5	$55.60	5.550%	$58.6858	$58.69	$58.70	$58.70
Purchase #6	$57.90	13.730%	$65.8497	$65.85	$65.85	$65.80
Purchase #7	$237.83	3.634%	$246.4727	$246.47	$246.45	$246.50
7 purchase totals =	$924.80		$983.9485	$983.95	$984.00	$983.90