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	$136.87	13.453%	$155.2831	$155.28	$155.30	$155.30
Purchase #2	$245.91	5.143%	$258.5572	$258.56	$258.55	$258.60
Purchase #3	$30.97	9.343%	$33.8635	$33.86	$33.85	$33.90
Purchase #4	$19.47	11.304%	$21.6709	$21.67	$21.65	$21.70
Purchase #5	$92.58	3.105%	$95.4546	$95.45	$95.45	$95.50
Purchase #6	$247.89	3.451%	$256.4447	$256.44	$256.45	$256.40
Purchase #7	$49.59	5.485%	$52.31	$52.31	$52.30	$52.30
7 purchase totals =	$823.28		$873.5840	$873.57	$873.55	$873.70