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	$35.86	11.244%	$39.8921	$39.89	$39.90	$39.90
Purchase #2	$106.72	13.765%	$121.41	$121.41	$121.40	$121.40
Purchase #3	$159.52	12.407%	$179.3116	$179.31	$179.30	$179.30
Purchase #4	$71.57	9.852%	$78.6211	$78.62	$78.60	$78.60
Purchase #5	$228.52	5.401%	$240.8624	$240.86	$240.85	$240.90
Purchase #6	$172.95	4.405%	$180.5684	$180.57	$180.55	$180.60
Purchase #7	$172.73	10.418%	$190.725	$190.73	$190.75	$190.70
7 purchase totals =	$947.87		$1,031.3906	$1,031.39	$1,031.35	$1,031.40