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	$194.63	12.170%	$218.3165	$218.32	$218.30	$218.30
Purchase #2	$152.48	3.324%	$157.5484	$157.55	$157.55	$157.50
Purchase #3	$62.86	7.593%	$67.633	$67.63	$67.65	$67.60
Purchase #4	$114.81	7.861%	$123.8352	$123.84	$123.85	$123.80
Purchase #5	$126.76	8.525%	$137.5663	$137.57	$137.55	$137.60
Purchase #6	$75.25	9.389%	$82.3152	$82.32	$82.30	$82.30
Purchase #7	$112.57	9.789%	$123.5895	$123.59	$123.60	$123.60
7 purchase totals =	$839.36		$910.8041	$910.82	$910.80	$910.70