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	$141.93	11.620%	$158.4223	$158.42	$158.40	$158.40
Purchase #2	$197.82	10.492%	$218.5753	$218.58	$218.60	$218.60
Purchase #3	$35.30	7.107%	$37.8088	$37.81	$37.80	$37.80
Purchase #4	$165.62	10.549%	$183.0913	$183.09	$183.10	$183.10
Purchase #5	$69.60	3.834%	$72.2685	$72.27	$72.25	$72.30
Purchase #6	$35.86	11.169%	$39.8652	$39.87	$39.85	$39.90
Purchase #7	$12.50	5.188%	$13.1485	$13.15	$13.15	$13.10
7 purchase totals =	$658.63		$723.1799	$723.19	$723.15	$723.20