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	$217.86	10.155%	$239.9837	$239.98	$240.00	$240.00
Purchase #2	$169.67	6.341%	$180.4288	$180.43	$180.45	$180.40
Purchase #3	$234.69	3.459%	$242.8079	$242.81	$242.80	$242.80
Purchase #4	$78.77	12.597%	$88.6927	$88.69	$88.70	$88.70
Purchase #5	$183.65	9.236%	$200.6119	$200.61	$200.60	$200.60
Purchase #6	$96.77	13.377%	$109.7149	$109.71	$109.70	$109.70
Purchase #7	$57.77	12.245%	$64.8439	$64.84	$64.85	$64.80
7 purchase totals =	$1,039.18		$1,127.0838	$1,127.07	$1,127.10	$1,127.00