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	$155.26	6.829%	$165.8627	$165.86	$165.85	$165.90
Purchase #2	$133.59	4.646%	$139.7966	$139.80	$139.80	$139.80
Purchase #3	$128.54	9.846%	$141.196	$141.20	$141.20	$141.20
Purchase #4	$35.52	8.105%	$38.3989	$38.40	$38.40	$38.40
Purchase #5	$172.69	6.279%	$183.5332	$183.53	$183.55	$183.50
Purchase #6	$115.72	11.749%	$129.3159	$129.32	$129.30	$129.30
Purchase #7	$90.45	10.790%	$100.2096	$100.21	$100.20	$100.20
7 purchase totals =	$831.77		$898.3129	$898.32	$898.30	$898.30