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	$25.74	5.367%	$27.1215	$27.12	$27.10	$27.10
Purchase #2	$95.37	10.737%	$105.6099	$105.61	$105.60	$105.60
Purchase #3	$76.63	4.538%	$80.1075	$80.11	$80.10	$80.10
Purchase #4	$32.83	3.615%	$34.0168	$34.02	$34.00	$34.00
Purchase #5	$93.42	7.384%	$100.3181	$100.32	$100.30	$100.30
Purchase #6	$44.43	8.699%	$48.295	$48.30	$48.30	$48.30
Purchase #7	$190.72	3.351%	$197.111	$197.11	$197.10	$197.10
7 purchase totals =	$559.14		$592.5798	$592.59	$592.50	$592.50