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	$60.82	9.109%	$66.3601	$66.36	$66.35	$66.40
Purchase #2	$237.48	10.821%	$263.1777	$263.18	$263.20	$263.20
Purchase #3	$172.25	12.387%	$193.5866	$193.59	$193.60	$193.60
Purchase #4	$199.54	9.159%	$217.8159	$217.82	$217.80	$217.80
Purchase #5	$116.46	5.691%	$123.0877	$123.09	$123.10	$123.10
Purchase #6	$240.46	6.533%	$256.1693	$256.17	$256.15	$256.20
Purchase #7	$91.35	9.791%	$100.2941	$100.29	$100.30	$100.30
7 purchase totals =	$1,118.36		$1,220.4914	$1,220.50	$1,220.50	$1,220.60