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	$248.25	11.337%	$276.3941	$276.39	$276.40	$276.40
Purchase #2	$117.74	4.503%	$123.0418	$123.04	$123.05	$123.00
Purchase #3	$178.32	12.508%	$200.6243	$200.62	$200.60	$200.60
Purchase #4	$187.37	11.328%	$208.5953	$208.60	$208.60	$208.60
Purchase #5	$122.46	9.817%	$134.4819	$134.48	$134.50	$134.50
Purchase #6	$155.41	8.733%	$168.982	$168.98	$169.00	$169.00
Purchase #7	$130.76	5.864%	$138.4278	$138.43	$138.45	$138.40
7 purchase totals =	$1,140.31		$1,250.5472	$1,250.54	$1,250.60	$1,250.50