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	$249.45	3.397%	$257.9238	$257.92	$257.90	$257.90
Purchase #2	$99.67	11.675%	$111.3065	$111.31	$111.30	$111.30
Purchase #3	$40.46	9.162%	$44.1669	$44.17	$44.15	$44.20
Purchase #4	$144.62	5.469%	$152.5293	$152.53	$152.55	$152.50
Purchase #5	$135.96	4.483%	$142.0551	$142.06	$142.05	$142.10
Purchase #6	$62.37	13.231%	$70.6222	$70.62	$70.60	$70.60
Purchase #7	$185.82	13.657%	$211.1974	$211.20	$211.20	$211.20
7 purchase totals =	$918.35		$989.8012	$989.81	$989.75	$989.80