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	$240.55	7.861%	$259.4596	$259.46	$259.45	$259.50
Purchase #2	$164.40	11.826%	$183.8419	$183.84	$183.85	$183.80
Purchase #3	$211.66	4.529%	$221.2461	$221.25	$221.25	$221.20
Purchase #4	$219.54	9.333%	$240.0297	$240.03	$240.05	$240.00
Purchase #5	$83.78	8.549%	$90.9424	$90.94	$90.95	$90.90
Purchase #6	$156.37	10.339%	$172.5371	$172.54	$172.55	$172.50
Purchase #7	$196.66	12.705%	$221.6457	$221.65	$221.65	$221.60
7 purchase totals =	$1,272.96		$1,389.7025	$1,389.71	$1,389.75	$1,389.50