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	$136.48	6.429%	$145.2543	$145.25	$145.25	$145.30
Purchase #2	$70.94	13.309%	$80.3814	$80.38	$80.40	$80.40
Purchase #3	$21.31	10.671%	$23.584	$23.58	$23.60	$23.60
Purchase #4	$40.26	5.372%	$42.4228	$42.42	$42.40	$42.40
Purchase #5	$175.67	11.692%	$196.2093	$196.21	$196.20	$196.20
Purchase #6	$45.42	4.141%	$47.3008	$47.30	$47.30	$47.30
Purchase #7	$111.58	8.440%	$120.9974	$121.00	$121.00	$121.00
7 purchase totals =	$601.66		$656.1500	$656.14	$656.15	$656.20