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	$32.54	4.230%	$33.9164	$33.92	$33.90	$33.90
Purchase #2	$187.91	4.521%	$196.4054	$196.41	$196.40	$196.40
Purchase #3	$56.33	10.552%	$62.2739	$62.27	$62.25	$62.30
Purchase #4	$109.40	6.357%	$116.3546	$116.35	$116.35	$116.40
Purchase #5	$87.29	5.712%	$92.276	$92.28	$92.30	$92.30
Purchase #6	$111.40	9.149%	$121.592	$121.59	$121.60	$121.60
Purchase #7	$41.79	5.117%	$43.9284	$43.93	$43.95	$43.90
7 purchase totals =	$626.66		$666.7467	$666.75	$666.75	$666.80