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	$121.90	12.860%	$137.5763	$137.58	$137.60	$137.60
Purchase #2	$152.84	10.573%	$168.9998	$169.00	$169.00	$169.00
Purchase #3	$116.67	8.756%	$126.8856	$126.89	$126.90	$126.90
Purchase #4	$97.61	9.575%	$106.9562	$106.96	$106.95	$107.00
Purchase #5	$86.62	3.815%	$89.9246	$89.92	$89.90	$89.90
Purchase #6	$122.57	12.123%	$137.4292	$137.43	$137.45	$137.40
Purchase #7	$180.50	5.541%	$190.5015	$190.50	$190.50	$190.50
7 purchase totals =	$878.71		$958.2732	$958.28	$958.30	$958.30