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	$121.69	13.367%	$137.9563	$137.96	$137.95	$138.00
Purchase #2	$246.35	11.580%	$274.8773	$274.88	$274.90	$274.90
Purchase #3	$229.35	9.475%	$251.0809	$251.08	$251.10	$251.10
Purchase #4	$203.97	9.524%	$223.3961	$223.40	$223.40	$223.40
Purchase #5	$95.57	5.617%	$100.9382	$100.94	$100.95	$100.90
Purchase #6	$177.77	10.549%	$196.523	$196.52	$196.50	$196.50
Purchase #7	$29.54	10.439%	$32.6237	$32.62	$32.60	$32.60
7 purchase totals =	$1,104.24		$1,217.3955	$1,217.40	$1,217.40	$1,217.40