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	$84.61	6.187%	$89.8448	$89.84	$89.85	$89.80
Purchase #2	$85.85	6.170%	$91.1469	$91.15	$91.15	$91.10
Purchase #3	$17.47	3.536%	$18.0877	$18.09	$18.10	$18.10
Purchase #4	$172.64	9.501%	$189.0425	$189.04	$189.05	$189.00
Purchase #5	$114.80	10.342%	$126.6726	$126.67	$126.65	$126.70
Purchase #6	$111.72	7.239%	$119.8074	$119.81	$119.80	$119.80
Purchase #7	$7.48	5.652%	$7.9028	$7.90	$7.90	$7.90
7 purchase totals =	$594.57		$642.5047	$642.50	$642.50	$642.40