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	$102.28	9.103%	$111.5905	$111.59	$111.60	$111.60
Purchase #2	$159.38	3.139%	$164.3829	$164.38	$164.40	$164.40
Purchase #3	$231.25	3.797%	$240.0306	$240.03	$240.05	$240.00
Purchase #4	$64.85	6.181%	$68.8584	$68.86	$68.85	$68.90
Purchase #5	$13.78	7.706%	$14.8419	$14.84	$14.85	$14.80
Purchase #6	$58.66	5.522%	$61.8992	$61.90	$61.90	$61.90
Purchase #7	$70.42	11.269%	$78.3556	$78.36	$78.35	$78.40
7 purchase totals =	$700.62		$739.9591	$739.96	$740.00	$740.00