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	$14.51	8.817%	$15.7893	$15.79	$15.80	$15.80
Purchase #2	$51.93	8.142%	$56.1581	$56.16	$56.15	$56.20
Purchase #3	$54.68	4.359%	$57.0635	$57.06	$57.05	$57.10
Purchase #4	$63.52	4.803%	$66.5709	$66.57	$66.55	$66.60
Purchase #5	$102.40	7.220%	$109.7933	$109.79	$109.80	$109.80
Purchase #6	$56.84	7.592%	$61.1553	$61.16	$61.15	$61.20
Purchase #7	$92.52	10.813%	$102.5242	$102.52	$102.50	$102.50
7 purchase totals =	$436.40		$469.0546	$469.05	$469.00	$469.20