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	$56.34	11.162%	$62.6287	$62.63	$62.65	$62.60
Purchase #2	$35.36	8.348%	$38.3119	$38.31	$38.30	$38.30
Purchase #3	$28.99	8.508%	$31.4565	$31.46	$31.45	$31.50
Purchase #4	$153.60	11.716%	$171.5958	$171.60	$171.60	$171.60
Purchase #5	$237.86	3.774%	$246.8368	$246.84	$246.85	$246.80
Purchase #6	$77.65	4.139%	$80.8639	$80.86	$80.85	$80.90
Purchase #7	$27.72	3.193%	$28.6051	$28.61	$28.60	$28.60
7 purchase totals =	$617.52		$660.2987	$660.31	$660.30	$660.30