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	$35.65	8.166%	$38.5612	$38.56	$38.55	$38.60
Purchase #2	$137.38	6.288%	$146.0185	$146.02	$146.00	$146.00
Purchase #3	$102.72	9.600%	$112.5811	$112.58	$112.60	$112.60
Purchase #4	$143.32	4.773%	$150.1607	$150.16	$150.15	$150.20
Purchase #5	$137.58	6.492%	$146.5117	$146.51	$146.50	$146.50
Purchase #6	$103.85	4.469%	$108.4911	$108.49	$108.50	$108.50
Purchase #7	$79.73	5.431%	$84.0601	$84.06	$84.05	$84.10
7 purchase totals =	$740.23		$786.3844	$786.38	$786.35	$786.50