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	$48.94	5.848%	$51.802	$51.80	$51.80	$51.80
Purchase #2	$102.43	9.705%	$112.3708	$112.37	$112.35	$112.40
Purchase #3	$106.92	4.153%	$111.3604	$111.36	$111.35	$111.40
Purchase #4	$102.31	9.223%	$111.7461	$111.75	$111.75	$111.70
Purchase #5	$228.60	5.798%	$241.8542	$241.85	$241.85	$241.90
Purchase #6	$40.29	7.425%	$43.2815	$43.28	$43.30	$43.30
Purchase #7	$37.96	9.338%	$41.5047	$41.50	$41.50	$41.50
7 purchase totals =	$667.45		$713.9197	$713.91	$713.90	$714.00