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	$16.90	8.714%	$18.3727	$18.37	$18.35	$18.40
Purchase #2	$13.96	3.868%	$14.5	$14.50	$14.50	$14.50
Purchase #3	$84.39	9.123%	$92.0889	$92.09	$92.10	$92.10
Purchase #4	$218.64	5.458%	$230.5734	$230.57	$230.55	$230.60
Purchase #5	$78.88	13.299%	$89.3703	$89.37	$89.35	$89.40
Purchase #6	$204.96	8.710%	$222.812	$222.81	$222.80	$222.80
Purchase #7	$141.66	12.377%	$159.1933	$159.19	$159.20	$159.20
7 purchase totals =	$759.39		$826.9106	$826.90	$826.85	$827.00