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	$139.71	13.784%	$158.9676	$158.97	$158.95	$159.00
Purchase #2	$51.65	9.409%	$56.5097	$56.51	$56.50	$56.50
Purchase #3	$135.87	5.849%	$143.817	$143.82	$143.80	$143.80
Purchase #4	$129.88	13.658%	$147.619	$147.62	$147.60	$147.60
Purchase #5	$73.50	11.577%	$82.0091	$82.01	$82.00	$82.00
Purchase #6	$196.70	9.726%	$215.831	$215.83	$215.85	$215.80
Purchase #7	$101.38	5.674%	$107.1323	$107.13	$107.15	$107.10
7 purchase totals =	$828.69		$911.8857	$911.89	$911.85	$911.80