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	$178.92	6.349%	$190.2796	$190.28	$190.30	$190.30
Purchase #2	$39.48	12.557%	$44.4375	$44.44	$44.45	$44.40
Purchase #3	$145.38	5.586%	$153.5009	$153.50	$153.50	$153.50
Purchase #4	$172.54	8.420%	$187.0679	$187.07	$187.05	$187.10
Purchase #5	$86.87	4.160%	$90.4838	$90.48	$90.50	$90.50
Purchase #6	$133.60	8.538%	$145.0068	$145.01	$145.00	$145.00
Purchase #7	$71.35	10.141%	$78.5856	$78.59	$78.60	$78.60
7 purchase totals =	$828.14		$889.3621	$889.37	$889.40	$889.40