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	$117.98	8.815%	$128.3799	$128.38	$128.40	$128.40
Purchase #2	$78.54	3.659%	$81.4138	$81.41	$81.40	$81.40
Purchase #3	$131.86	8.854%	$143.5349	$143.53	$143.55	$143.50
Purchase #4	$19.85	12.462%	$22.3237	$22.32	$22.30	$22.30
Purchase #5	$49.76	3.676%	$51.5892	$51.59	$51.60	$51.60
Purchase #6	$77.78	11.563%	$86.7737	$86.77	$86.75	$86.80
Purchase #7	$80.58	3.522%	$83.418	$83.42	$83.40	$83.40
7 purchase totals =	$556.35		$597.4332	$597.42	$597.40	$597.40