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	$149.78	11.359%	$166.7935	$166.79	$166.80	$166.80
Purchase #2	$218.43	10.443%	$241.2406	$241.24	$241.25	$241.20
Purchase #3	$72.37	12.832%	$81.6565	$81.66	$81.65	$81.70
Purchase #4	$225.60	4.730%	$236.2709	$236.27	$236.25	$236.30
Purchase #5	$140.43	11.538%	$156.6328	$156.63	$156.65	$156.60
Purchase #6	$216.31	9.734%	$237.3656	$237.37	$237.35	$237.40
Purchase #7	$111.72	10.654%	$123.6226	$123.62	$123.60	$123.60
7 purchase totals =	$1,134.64		$1,243.5825	$1,243.58	$1,243.55	$1,243.60