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	$24.49	5.691%	$25.8837	$25.88	$25.90	$25.90
Purchase #2	$55.59	12.612%	$62.601	$62.60	$62.60	$62.60
Purchase #3	$147.66	12.427%	$166.0097	$166.01	$166.00	$166.00
Purchase #4	$206.75	11.260%	$230.0301	$230.03	$230.05	$230.00
Purchase #5	$145.71	12.742%	$164.2764	$164.28	$164.30	$164.30
Purchase #6	$122.90	13.810%	$139.8725	$139.87	$139.85	$139.90
Purchase #7	$158.50	12.797%	$178.7832	$178.78	$178.80	$178.80
7 purchase totals =	$861.60		$967.4566	$967.45	$967.50	$967.50