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	$39.60	9.853%	$43.5018	$43.50	$43.50	$43.50
Purchase #2	$180.60	10.435%	$199.4456	$199.45	$199.45	$199.40
Purchase #3	$34.39	11.535%	$38.3569	$38.36	$38.35	$38.40
Purchase #4	$41.36	6.210%	$43.9285	$43.93	$43.95	$43.90
Purchase #5	$73.35	6.339%	$77.9997	$78.00	$78.00	$78.00
Purchase #6	$182.31	4.675%	$190.833	$190.83	$190.85	$190.80
Purchase #7	$104.91	10.495%	$115.9203	$115.92	$115.90	$115.90
7 purchase totals =	$656.52		$709.9858	$709.99	$710.00	$709.90