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	$39.53	8.376%	$42.841	$42.84	$42.85	$42.80
Purchase #2	$116.53	8.522%	$126.4607	$126.46	$126.45	$126.50
Purchase #3	$34.61	10.356%	$38.1942	$38.19	$38.20	$38.20
Purchase #4	$33.50	6.216%	$35.5824	$35.58	$35.60	$35.60
Purchase #5	$155.95	5.457%	$164.4602	$164.46	$164.45	$164.50
Purchase #6	$138.81	12.561%	$156.2459	$156.25	$156.25	$156.20
Purchase #7	$219.63	9.752%	$241.0483	$241.05	$241.05	$241.00
7 purchase totals =	$738.56		$804.8327	$804.83	$804.85	$804.80