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	$183.27	13.489%	$207.9913	$207.99	$208.00	$208.00
Purchase #2	$19.27	10.241%	$21.2434	$21.24	$21.25	$21.20
Purchase #3	$135.60	13.111%	$153.3785	$153.38	$153.40	$153.40
Purchase #4	$136.70	4.249%	$142.5084	$142.51	$142.50	$142.50
Purchase #5	$86.27	4.117%	$89.8217	$89.82	$89.80	$89.80
Purchase #6	$90.60	13.754%	$103.0611	$103.06	$103.05	$103.10
Purchase #7	$226.41	13.651%	$257.3172	$257.32	$257.30	$257.30
7 purchase totals =	$878.12		$975.3216	$975.32	$975.30	$975.30