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	$38.63	10.866%	$42.8275	$42.83	$42.85	$42.80
Purchase #2	$249.42	10.225%	$274.9232	$274.92	$274.90	$274.90
Purchase #3	$169.55	10.756%	$187.7868	$187.79	$187.80	$187.80
Purchase #4	$8.30	12.202%	$9.3128	$9.31	$9.30	$9.30
Purchase #5	$105.38	7.149%	$112.9136	$112.91	$112.90	$112.90
Purchase #6	$17.47	3.805%	$18.1347	$18.13	$18.15	$18.10
Purchase #7	$183.99	6.784%	$196.4719	$196.47	$196.45	$196.50
7 purchase totals =	$772.74		$842.3705	$842.36	$842.35	$842.30