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	$108.61	13.380%	$123.142	$123.14	$123.15	$123.10
Purchase #2	$233.71	6.529%	$248.9689	$248.97	$248.95	$249.00
Purchase #3	$17.43	3.206%	$17.9888	$17.99	$18.00	$18.00
Purchase #4	$55.57	12.857%	$62.7146	$62.71	$62.70	$62.70
Purchase #5	$10.95	5.829%	$11.5883	$11.59	$11.60	$11.60
Purchase #6	$87.89	10.242%	$96.8917	$96.89	$96.90	$96.90
Purchase #7	$102.97	13.229%	$116.5919	$116.59	$116.60	$116.60
7 purchase totals =	$617.13		$677.8862	$677.88	$677.90	$677.90