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	$102.94	6.160%	$109.2811	$109.28	$109.30	$109.30
Purchase #2	$139.82	3.567%	$144.8074	$144.81	$144.80	$144.80
Purchase #3	$25.85	6.510%	$27.5328	$27.53	$27.55	$27.50
Purchase #4	$138.93	13.622%	$157.855	$157.86	$157.85	$157.90
Purchase #5	$28.44	13.848%	$32.3784	$32.38	$32.40	$32.40
Purchase #6	$51.77	9.374%	$56.6229	$56.62	$56.60	$56.60
Purchase #7	$129.73	7.528%	$139.4961	$139.50	$139.50	$139.50
7 purchase totals =	$617.48		$667.9737	$667.98	$668.00	$668.00