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	$133.72	4.652%	$139.9407	$139.94	$139.95	$139.90
Purchase #2	$201.87	8.490%	$219.0088	$219.01	$219.00	$219.00
Purchase #3	$163.50	13.215%	$185.1065	$185.11	$185.10	$185.10
Purchase #4	$127.65	5.638%	$134.8469	$134.85	$134.85	$134.80
Purchase #5	$98.67	12.611%	$111.1133	$111.11	$111.10	$111.10
Purchase #6	$35.57	13.188%	$40.261	$40.26	$40.25	$40.30
Purchase #7	$30.87	5.431%	$32.5465	$32.55	$32.55	$32.50
7 purchase totals =	$791.85		$862.8237	$862.83	$862.80	$862.70