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	$38.77	4.583%	$40.5468	$40.55	$40.55	$40.50
Purchase #2	$151.83	12.855%	$171.3477	$171.35	$171.35	$171.30
Purchase #3	$129.78	6.527%	$138.2507	$138.25	$138.25	$138.30
Purchase #4	$235.60	10.505%	$260.3498	$260.35	$260.35	$260.30
Purchase #5	$100.91	9.305%	$110.2997	$110.30	$110.30	$110.30
Purchase #6	$86.65	6.719%	$92.472	$92.47	$92.45	$92.50
Purchase #7	$34.46	11.589%	$38.4536	$38.45	$38.45	$38.50
7 purchase totals =	$778.00		$851.7203	$851.72	$851.70	$851.70