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	$16.31	6.532%	$17.3754	$17.38	$17.40	$17.40
Purchase #2	$158.94	4.731%	$166.4595	$166.46	$166.45	$166.50
Purchase #3	$117.85	4.510%	$123.165	$123.17	$123.15	$123.20
Purchase #4	$25.46	13.619%	$28.9274	$28.93	$28.95	$28.90
Purchase #5	$45.32	13.509%	$51.4423	$51.44	$51.45	$51.40
Purchase #6	$29.64	9.269%	$32.3873	$32.39	$32.40	$32.40
Purchase #7	$140.48	3.117%	$144.8588	$144.86	$144.85	$144.90
7 purchase totals =	$534.00		$564.6157	$564.63	$564.65	$564.70