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	$114.64	8.576%	$124.4715	$124.47	$124.45	$124.50
Purchase #2	$200.25	13.747%	$227.7784	$227.78	$227.80	$227.80
Purchase #3	$180.73	8.633%	$196.3324	$196.33	$196.35	$196.30
Purchase #4	$121.36	13.670%	$137.9499	$137.95	$137.95	$137.90
Purchase #5	$164.64	13.478%	$186.8302	$186.83	$186.85	$186.80
Purchase #6	$221.76	4.190%	$231.0517	$231.05	$231.05	$231.10
Purchase #7	$225.69	3.500%	$233.5892	$233.59	$233.60	$233.60
7 purchase totals =	$1,229.07		$1,338.0033	$1,338.00	$1,338.05	$1,338.00