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	$5.97	8.641%	$6.4859	$6.49	$6.50	$6.50
Purchase #2	$162.25	6.532%	$172.8482	$172.85	$172.85	$172.80
Purchase #3	$209.80	8.607%	$227.8575	$227.86	$227.85	$227.90
Purchase #4	$175.92	8.512%	$190.8943	$190.89	$190.90	$190.90
Purchase #5	$178.52	5.795%	$188.8652	$188.87	$188.85	$188.90
Purchase #6	$103.25	13.597%	$117.2889	$117.29	$117.30	$117.30
Purchase #7	$162.96	10.160%	$179.5167	$179.52	$179.50	$179.50
7 purchase totals =	$998.67		$1,083.7567	$1,083.77	$1,083.75	$1,083.80