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	$66.58	6.828%	$71.1261	$71.13	$71.15	$71.10
Purchase #2	$104.96	6.709%	$112.0018	$112.00	$112.00	$112.00
Purchase #3	$12.96	10.311%	$14.2963	$14.30	$14.30	$14.30
Purchase #4	$230.78	13.255%	$261.3699	$261.37	$261.35	$261.40
Purchase #5	$217.74	5.420%	$229.5415	$229.54	$229.55	$229.50
Purchase #6	$87.64	3.645%	$90.8345	$90.83	$90.85	$90.80
Purchase #7	$66.89	12.741%	$75.4125	$75.41	$75.40	$75.40
7 purchase totals =	$787.55		$854.5826	$854.58	$854.60	$854.50