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	$126.83	10.693%	$140.3919	$140.39	$140.40	$140.40
Purchase #2	$208.91	7.774%	$225.1507	$225.15	$225.15	$225.20
Purchase #3	$34.64	6.304%	$36.8237	$36.82	$36.80	$36.80
Purchase #4	$40.94	5.133%	$43.0415	$43.04	$43.05	$43.00
Purchase #5	$51.79	3.382%	$53.5415	$53.54	$53.55	$53.50
Purchase #6	$117.80	7.419%	$126.5396	$126.54	$126.55	$126.50
Purchase #7	$43.52	4.546%	$45.4984	$45.50	$45.50	$45.50
7 purchase totals =	$624.43		$670.9873	$670.98	$671.00	$670.90