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	$156.84	12.572%	$176.5579	$176.56	$176.55	$176.60
Purchase #2	$16.65	7.871%	$17.9605	$17.96	$17.95	$18.00
Purchase #3	$83.56	8.303%	$90.498	$90.50	$90.50	$90.50
Purchase #4	$58.71	13.301%	$66.519	$66.52	$66.50	$66.50
Purchase #5	$41.27	5.105%	$43.3768	$43.38	$43.40	$43.40
Purchase #6	$41.38	8.418%	$44.8634	$44.86	$44.85	$44.90
Purchase #7	$146.44	4.162%	$152.5348	$152.53	$152.55	$152.50
7 purchase totals =	$544.85		$592.3104	$592.31	$592.30	$592.40