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	$167.89	7.255%	$180.0704	$180.07	$180.05	$180.10
Purchase #2	$112.53	5.397%	$118.6032	$118.60	$118.60	$118.60
Purchase #3	$209.48	13.713%	$238.206	$238.21	$238.20	$238.20
Purchase #4	$241.82	5.286%	$254.6026	$254.60	$254.60	$254.60
Purchase #5	$7.83	10.410%	$8.6451	$8.65	$8.65	$8.60
Purchase #6	$82.60	8.255%	$89.4186	$89.42	$89.40	$89.40
Purchase #7	$168.59	4.863%	$176.7885	$176.79	$176.80	$176.80
7 purchase totals =	$990.74		$1,066.3344	$1,066.34	$1,066.30	$1,066.30