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	$12.71	9.668%	$13.9388	$13.94	$13.95	$13.90
Purchase #2	$140.39	6.710%	$149.8102	$149.81	$149.80	$149.80
Purchase #3	$36.74	10.260%	$40.5095	$40.51	$40.50	$40.50
Purchase #4	$27.61	4.528%	$28.8602	$28.86	$28.85	$28.90
Purchase #5	$209.99	13.768%	$238.9014	$238.90	$238.90	$238.90
Purchase #6	$38.63	12.439%	$43.4352	$43.44	$43.45	$43.40
Purchase #7	$156.83	10.171%	$172.7812	$172.78	$172.80	$172.80
7 purchase totals =	$622.90		$688.2365	$688.24	$688.25	$688.20