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	$210.83	3.168%	$217.5091	$217.51	$217.50	$217.50
Purchase #2	$138.63	4.322%	$144.6216	$144.62	$144.60	$144.60
Purchase #3	$133.51	5.272%	$140.5486	$140.55	$140.55	$140.50
Purchase #4	$37.37	5.356%	$39.3715	$39.37	$39.35	$39.40
Purchase #5	$192.45	8.346%	$208.5119	$208.51	$208.50	$208.50
Purchase #6	$102.84	11.747%	$114.9206	$114.92	$114.90	$114.90
Purchase #7	$182.67	4.732%	$191.3139	$191.31	$191.30	$191.30
7 purchase totals =	$998.30		$1,056.7972	$1,056.79	$1,056.70	$1,056.70