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	$75.71	4.217%	$78.9027	$78.90	$78.90	$78.90
Purchase #2	$16.89	13.855%	$19.2301	$19.23	$19.25	$19.20
Purchase #3	$161.63	7.387%	$173.5696	$173.57	$173.55	$173.60
Purchase #4	$55.63	10.555%	$61.5017	$61.50	$61.50	$61.50
Purchase #5	$152.86	7.397%	$164.1671	$164.17	$164.15	$164.20
Purchase #6	$66.34	10.856%	$73.5419	$73.54	$73.55	$73.50
Purchase #7	$103.85	6.338%	$110.432	$110.43	$110.45	$110.40
7 purchase totals =	$632.91		$681.3451	$681.34	$681.35	$681.30