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	$122.98	13.396%	$139.4544	$139.45	$139.45	$139.50
Purchase #2	$128.60	10.852%	$142.5557	$142.56	$142.55	$142.60
Purchase #3	$185.71	13.522%	$210.8217	$210.82	$210.80	$210.80
Purchase #4	$96.78	6.173%	$102.7542	$102.75	$102.75	$102.80
Purchase #5	$160.98	6.577%	$171.5677	$171.57	$171.55	$171.60
Purchase #6	$77.29	4.458%	$80.7356	$80.74	$80.75	$80.70
Purchase #7	$250.82	7.271%	$269.0571	$269.06	$269.05	$269.10
7 purchase totals =	$1,023.16		$1,116.9464	$1,116.95	$1,116.90	$1,117.10