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	$28.40	6.132%	$30.1415	$30.14	$30.15	$30.10
Purchase #2	$106.77	5.789%	$112.9509	$112.95	$112.95	$113.00
Purchase #3	$43.52	4.789%	$45.6042	$45.60	$45.60	$45.60
Purchase #4	$47.34	9.156%	$51.6745	$51.67	$51.65	$51.70
Purchase #5	$10.59	6.631%	$11.2922	$11.29	$11.30	$11.30
Purchase #6	$248.59	6.847%	$265.611	$265.61	$265.60	$265.60
Purchase #7	$13.74	12.352%	$15.4372	$15.44	$15.45	$15.40
7 purchase totals =	$498.95		$532.7115	$532.70	$532.70	$532.70