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	$144.78	9.647%	$158.7469	$158.75	$158.75	$158.70
Purchase #2	$78.37	8.578%	$85.0926	$85.09	$85.10	$85.10
Purchase #3	$80.91	10.584%	$89.4735	$89.47	$89.45	$89.50
Purchase #4	$142.33	13.706%	$161.8377	$161.84	$161.85	$161.80
Purchase #5	$29.51	10.850%	$32.7118	$32.71	$32.70	$32.70
Purchase #6	$136.39	13.347%	$154.594	$154.59	$154.60	$154.60
Purchase #7	$131.71	10.841%	$145.9887	$145.99	$146.00	$146.00
7 purchase totals =	$744.00		$828.4452	$828.44	$828.45	$828.40