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	$132.83	4.670%	$139.0332	$139.03	$139.05	$139.00
Purchase #2	$35.48	5.585%	$37.4616	$37.46	$37.45	$37.50
Purchase #3	$9.64	5.537%	$10.1738	$10.17	$10.15	$10.20
Purchase #4	$195.72	12.534%	$220.2515	$220.25	$220.25	$220.30
Purchase #5	$184.64	6.620%	$196.8632	$196.86	$196.85	$196.90
Purchase #6	$185.67	11.247%	$206.5523	$206.55	$206.55	$206.60
Purchase #7	$45.91	5.537%	$48.452	$48.45	$48.45	$48.50
7 purchase totals =	$789.89		$858.7876	$858.77	$858.75	$859.00