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	$87.82	5.802%	$92.9153	$92.92	$92.90	$92.90
Purchase #2	$200.52	11.233%	$223.0444	$223.04	$223.05	$223.00
Purchase #3	$144.55	8.267%	$156.4999	$156.50	$156.50	$156.50
Purchase #4	$131.83	8.256%	$142.7139	$142.71	$142.70	$142.70
Purchase #5	$156.69	11.230%	$174.2863	$174.29	$174.30	$174.30
Purchase #6	$157.30	3.466%	$162.752	$162.75	$162.75	$162.80
Purchase #7	$33.64	9.441%	$36.816	$36.82	$36.80	$36.80
7 purchase totals =	$912.35		$989.0278	$989.03	$989.00	$989.00