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	$5.81	10.448%	$6.417	$6.42	$6.40	$6.40
Purchase #2	$198.98	4.567%	$208.0674	$208.07	$208.05	$208.10
Purchase #3	$193.61	6.172%	$205.5596	$205.56	$205.55	$205.60
Purchase #4	$196.39	12.263%	$220.4733	$220.47	$220.45	$220.50
Purchase #5	$187.80	4.432%	$196.1233	$196.12	$196.10	$196.10
Purchase #6	$56.46	4.679%	$59.1018	$59.10	$59.10	$59.10
Purchase #7	$34.73	9.781%	$38.1269	$38.13	$38.15	$38.10
7 purchase totals =	$873.78		$933.8693	$933.87	$933.80	$933.90