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	$145.27	10.289%	$160.2168	$160.22	$160.20	$160.20
Purchase #2	$87.32	10.648%	$96.6178	$96.62	$96.60	$96.60
Purchase #3	$35.85	12.670%	$40.3922	$40.39	$40.40	$40.40
Purchase #4	$108.37	9.189%	$118.3281	$118.33	$118.35	$118.30
Purchase #5	$134.36	12.676%	$151.3915	$151.39	$151.40	$151.40
Purchase #6	$75.90	12.523%	$85.405	$85.41	$85.40	$85.40
Purchase #7	$156.99	5.853%	$166.1786	$166.18	$166.20	$166.20
7 purchase totals =	$744.06		$818.5300	$818.54	$818.55	$818.50