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	$10.69	13.608%	$12.1447	$12.14	$12.15	$12.10
Purchase #2	$69.56	11.397%	$77.4878	$77.49	$77.50	$77.50
Purchase #3	$86.72	3.214%	$89.5072	$89.51	$89.50	$89.50
Purchase #4	$75.48	9.854%	$82.9178	$82.92	$82.90	$82.90
Purchase #5	$174.93	12.359%	$196.5496	$196.55	$196.55	$196.50
Purchase #6	$49.81	3.324%	$51.4657	$51.47	$51.45	$51.50
Purchase #7	$240.88	4.724%	$252.2592	$252.26	$252.25	$252.30
7 purchase totals =	$708.07		$762.3320	$762.34	$762.30	$762.30