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	$20.68	4.808%	$21.6743	$21.67	$21.65	$21.70
Purchase #2	$41.79	5.161%	$43.9468	$43.95	$43.95	$43.90
Purchase #3	$38.71	5.663%	$40.9021	$40.90	$40.90	$40.90
Purchase #4	$39.88	10.330%	$43.9996	$44.00	$44.00	$44.00
Purchase #5	$177.70	4.351%	$185.4317	$185.43	$185.45	$185.40
Purchase #6	$248.94	6.147%	$264.2423	$264.24	$264.25	$264.20
Purchase #7	$157.75	13.204%	$178.5793	$178.58	$178.60	$178.60
7 purchase totals =	$725.45		$778.7761	$778.77	$778.80	$778.70