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	$34.84	11.193%	$38.7396	$38.74	$38.75	$38.70
Purchase #2	$136.44	5.276%	$143.6386	$143.64	$143.65	$143.60
Purchase #3	$107.75	5.263%	$113.4209	$113.42	$113.40	$113.40
Purchase #4	$61.90	13.361%	$70.1705	$70.17	$70.15	$70.20
Purchase #5	$116.90	5.533%	$123.3681	$123.37	$123.35	$123.40
Purchase #6	$12.43	12.620%	$13.9987	$14.00	$14.00	$14.00
Purchase #7	$176.55	11.515%	$196.8797	$196.88	$196.90	$196.90
7 purchase totals =	$646.81		$700.2161	$700.22	$700.20	$700.20