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	$123.49	6.858%	$131.9589	$131.96	$131.95	$132.00
Purchase #2	$136.45	10.570%	$150.8728	$150.87	$150.85	$150.90
Purchase #3	$100.43	5.365%	$105.8181	$105.82	$105.80	$105.80
Purchase #4	$89.96	10.482%	$99.3896	$99.39	$99.40	$99.40
Purchase #5	$183.31	9.290%	$200.3395	$200.34	$200.35	$200.30
Purchase #6	$52.89	3.187%	$54.5756	$54.58	$54.60	$54.60
Purchase #7	$173.44	11.283%	$193.0092	$193.01	$193.00	$193.00
7 purchase totals =	$859.97		$935.9637	$935.97	$935.95	$936.00