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	$154.69	6.625%	$164.9382	$164.94	$164.95	$164.90
Purchase #2	$48.31	13.449%	$54.8072	$54.81	$54.80	$54.80
Purchase #3	$140.85	13.863%	$160.376	$160.38	$160.40	$160.40
Purchase #4	$63.96	5.705%	$67.6089	$67.61	$67.60	$67.60
Purchase #5	$161.28	12.607%	$181.6126	$181.61	$181.60	$181.60
Purchase #6	$114.51	6.606%	$122.0745	$122.07	$122.05	$122.10
Purchase #7	$199.79	13.411%	$226.5838	$226.58	$226.60	$226.60
7 purchase totals =	$883.39		$978.0012	$978.00	$978.00	$978.00