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	$92.60	13.229%	$104.8501	$104.85	$104.85	$104.90
Purchase #2	$132.32	10.348%	$146.0125	$146.01	$146.00	$146.00
Purchase #3	$90.88	6.181%	$96.4973	$96.50	$96.50	$96.50
Purchase #4	$136.39	13.184%	$154.3717	$154.37	$154.35	$154.40
Purchase #5	$117.94	6.125%	$125.1638	$125.16	$125.15	$125.20
Purchase #6	$55.68	7.595%	$59.9089	$59.91	$59.90	$59.90
Purchase #7	$208.28	8.237%	$225.436	$225.44	$225.45	$225.40
7 purchase totals =	$834.09		$912.2403	$912.24	$912.20	$912.30