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	$95.51	5.168%	$100.446	$100.45	$100.45	$100.40
Purchase #2	$50.86	9.307%	$55.5935	$55.59	$55.60	$55.60
Purchase #3	$86.90	12.871%	$98.0849	$98.08	$98.10	$98.10
Purchase #4	$127.97	13.547%	$145.3061	$145.31	$145.30	$145.30
Purchase #5	$168.43	13.318%	$190.8615	$190.86	$190.85	$190.90
Purchase #6	$188.90	7.184%	$202.4706	$202.47	$202.45	$202.50
Purchase #7	$23.93	5.623%	$25.2756	$25.28	$25.30	$25.30
7 purchase totals =	$742.50		$818.0382	$818.04	$818.05	$818.10