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	$18.68	7.482%	$20.0776	$20.08	$20.10	$20.10
Purchase #2	$169.43	10.667%	$187.5031	$187.50	$187.50	$187.50
Purchase #3	$98.67	13.326%	$111.8188	$111.82	$111.80	$111.80
Purchase #4	$72.51	11.184%	$80.6195	$80.62	$80.60	$80.60
Purchase #5	$85.91	9.254%	$93.8601	$93.86	$93.85	$93.90
Purchase #6	$76.69	11.636%	$85.6136	$85.61	$85.60	$85.60
Purchase #7	$95.91	9.195%	$104.7289	$104.73	$104.75	$104.70
7 purchase totals =	$617.80		$684.2216	$684.22	$684.20	$684.20