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	$7.75	6.705%	$8.2696	$8.27	$8.25	$8.30
Purchase #2	$178.35	10.204%	$196.5488	$196.55	$196.55	$196.50
Purchase #3	$153.67	3.458%	$158.9839	$158.98	$159.00	$159.00
Purchase #4	$54.97	11.457%	$61.2679	$61.27	$61.25	$61.30
Purchase #5	$157.26	9.484%	$172.1745	$172.17	$172.15	$172.20
Purchase #6	$44.36	8.772%	$48.2513	$48.25	$48.25	$48.30
Purchase #7	$207.33	9.567%	$227.1653	$227.17	$227.15	$227.20
7 purchase totals =	$803.69		$872.6613	$872.66	$872.60	$872.80