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	$81.26	3.194%	$83.8554	$83.86	$83.85	$83.90
Purchase #2	$82.92	7.442%	$89.0909	$89.09	$89.10	$89.10
Purchase #3	$183.87	6.215%	$195.2975	$195.30	$195.30	$195.30
Purchase #4	$36.49	10.239%	$40.2262	$40.23	$40.25	$40.20
Purchase #5	$156.56	3.849%	$162.586	$162.59	$162.60	$162.60
Purchase #6	$213.72	13.151%	$241.8263	$241.83	$241.85	$241.80
Purchase #7	$243.85	7.377%	$261.8388	$261.84	$261.85	$261.80
7 purchase totals =	$998.67		$1,074.7211	$1,074.74	$1,074.80	$1,074.70