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	$131.36	9.370%	$143.6684	$143.67	$143.65	$143.70
Purchase #2	$119.45	7.265%	$128.128	$128.13	$128.15	$128.10
Purchase #3	$61.59	7.191%	$66.0189	$66.02	$66.00	$66.00
Purchase #4	$62.82	13.179%	$71.099	$71.10	$71.10	$71.10
Purchase #5	$123.35	13.121%	$139.5348	$139.53	$139.55	$139.50
Purchase #6	$96.52	8.730%	$104.9462	$104.95	$104.95	$104.90
Purchase #7	$219.85	3.516%	$227.5799	$227.58	$227.60	$227.60
7 purchase totals =	$814.94		$880.9752	$880.98	$881.00	$880.90