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	$39.50	3.213%	$40.7691	$40.77	$40.75	$40.80
Purchase #2	$133.40	8.204%	$144.3441	$144.34	$144.35	$144.30
Purchase #3	$137.49	9.240%	$150.1941	$150.19	$150.20	$150.20
Purchase #4	$36.49	8.465%	$39.5789	$39.58	$39.60	$39.60
Purchase #5	$96.93	5.492%	$102.2534	$102.25	$102.25	$102.30
Purchase #6	$92.93	13.386%	$105.3696	$105.37	$105.35	$105.40
Purchase #7	$113.50	8.378%	$123.009	$123.01	$123.00	$123.00
7 purchase totals =	$650.24		$705.5182	$705.51	$705.50	$705.60