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	$52.54	8.461%	$56.9854	$56.99	$57.00	$57.00
Purchase #2	$154.92	3.626%	$160.5374	$160.54	$160.55	$160.50
Purchase #3	$84.75	6.136%	$89.9503	$89.95	$89.95	$90.00
Purchase #4	$119.93	6.692%	$127.9557	$127.96	$127.95	$128.00
Purchase #5	$136.44	10.616%	$150.9245	$150.92	$150.90	$150.90
Purchase #6	$180.86	8.455%	$196.1517	$196.15	$196.15	$196.20
Purchase #7	$134.37	6.763%	$143.4574	$143.46	$143.45	$143.50
7 purchase totals =	$863.81		$925.9624	$925.97	$925.95	$926.10