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	$53.59	7.473%	$57.5948	$57.59	$57.60	$57.60
Purchase #2	$108.85	9.851%	$119.5728	$119.57	$119.55	$119.60
Purchase #3	$117.39	8.616%	$127.5043	$127.50	$127.50	$127.50
Purchase #4	$172.65	10.233%	$190.3173	$190.32	$190.30	$190.30
Purchase #5	$122.80	11.753%	$137.2327	$137.23	$137.25	$137.20
Purchase #6	$68.49	4.575%	$71.6234	$71.62	$71.60	$71.60
Purchase #7	$50.89	3.250%	$52.5439	$52.54	$52.55	$52.50
7 purchase totals =	$694.66		$756.3892	$756.37	$756.35	$756.30