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	$27.83	13.329%	$31.5395	$31.54	$31.55	$31.50
Purchase #2	$33.32	13.518%	$37.8242	$37.82	$37.80	$37.80
Purchase #3	$126.88	5.493%	$133.8495	$133.85	$133.85	$133.80
Purchase #4	$69.61	10.153%	$76.6775	$76.68	$76.70	$76.70
Purchase #5	$218.63	5.472%	$230.5934	$230.59	$230.60	$230.60
Purchase #6	$247.93	8.605%	$269.2644	$269.26	$269.25	$269.30
Purchase #7	$214.94	3.414%	$222.2781	$222.28	$222.30	$222.30
7 purchase totals =	$939.14		$1,002.0266	$1,002.02	$1,002.05	$1,002.00