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	$153.35	12.280%	$172.1814	$172.18	$172.20	$172.20
Purchase #2	$171.71	4.236%	$178.9836	$178.98	$179.00	$179.00
Purchase #3	$7.83	9.520%	$8.5754	$8.58	$8.60	$8.60
Purchase #4	$162.69	5.800%	$172.126	$172.13	$172.15	$172.10
Purchase #5	$164.40	11.792%	$183.786	$183.79	$183.80	$183.80
Purchase #6	$52.60	8.664%	$57.1573	$57.16	$57.15	$57.20
Purchase #7	$104.56	7.570%	$112.4752	$112.48	$112.50	$112.50
7 purchase totals =	$817.14		$885.2849	$885.30	$885.40	$885.40