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	$241.70	12.229%	$271.2575	$271.26	$271.25	$271.30
Purchase #2	$27.70	12.164%	$31.0694	$31.07	$31.05	$31.10
Purchase #3	$203.30	8.422%	$220.4219	$220.42	$220.40	$220.40
Purchase #4	$141.71	7.126%	$151.8083	$151.81	$151.80	$151.80
Purchase #5	$105.85	12.453%	$119.0315	$119.03	$119.05	$119.00
Purchase #6	$99.97	5.848%	$105.8162	$105.82	$105.80	$105.80
Purchase #7	$231.66	10.666%	$256.3689	$256.37	$256.35	$256.40
7 purchase totals =	$1,051.89		$1,155.7737	$1,155.78	$1,155.70	$1,155.80