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	$38.50	11.215%	$42.8178	$42.82	$42.80	$42.80
Purchase #2	$18.57	13.746%	$21.1226	$21.12	$21.10	$21.10
Purchase #3	$143.27	13.874%	$163.1473	$163.15	$163.15	$163.10
Purchase #4	$107.62	4.125%	$112.0593	$112.06	$112.05	$112.10
Purchase #5	$22.86	7.588%	$24.5946	$24.59	$24.60	$24.60
Purchase #6	$59.76	13.843%	$68.0326	$68.03	$68.05	$68.00
Purchase #7	$215.81	9.131%	$235.5156	$235.52	$235.50	$235.50
7 purchase totals =	$606.39		$667.2898	$667.29	$667.25	$667.20