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	$232.56	13.172%	$263.1928	$263.19	$263.20	$263.20
Purchase #2	$214.25	10.647%	$237.0612	$237.06	$237.05	$237.10
Purchase #3	$101.41	13.329%	$114.9269	$114.93	$114.95	$114.90
Purchase #4	$35.66	13.575%	$40.5008	$40.50	$40.50	$40.50
Purchase #5	$101.52	4.213%	$105.797	$105.80	$105.80	$105.80
Purchase #6	$12.65	9.347%	$13.8324	$13.83	$13.85	$13.80
Purchase #7	$217.45	10.862%	$241.0694	$241.07	$241.05	$241.10
7 purchase totals =	$915.50		$1,016.3805	$1,016.38	$1,016.40	$1,016.40