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	$69.41	13.517%	$78.7921	$78.79	$78.80	$78.80
Purchase #2	$59.46	4.308%	$62.0215	$62.02	$62.00	$62.00
Purchase #3	$35.95	10.155%	$39.6007	$39.60	$39.60	$39.60
Purchase #4	$238.31	9.246%	$260.3441	$260.34	$260.35	$260.30
Purchase #5	$59.83	8.424%	$64.8701	$64.87	$64.85	$64.90
Purchase #6	$43.45	10.823%	$48.1526	$48.15	$48.15	$48.20
Purchase #7	$178.34	12.517%	$200.6628	$200.66	$200.65	$200.70
7 purchase totals =	$684.75		$754.4439	$754.43	$754.40	$754.50