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	$46.52	12.872%	$52.5081	$52.51	$52.50	$52.50
Purchase #2	$168.55	5.619%	$178.0208	$178.02	$178.00	$178.00
Purchase #3	$171.70	7.396%	$184.3989	$184.40	$184.40	$184.40
Purchase #4	$131.47	8.748%	$142.971	$142.97	$142.95	$143.00
Purchase #5	$67.54	7.508%	$72.6109	$72.61	$72.60	$72.60
Purchase #6	$11.33	10.311%	$12.4982	$12.50	$12.50	$12.50
Purchase #7	$168.42	6.391%	$179.1837	$179.18	$179.20	$179.20
7 purchase totals =	$765.53		$822.1916	$822.19	$822.15	$822.20