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	$17.61	10.861%	$19.5226	$19.52	$19.50	$19.50
Purchase #2	$72.73	13.699%	$82.6933	$82.69	$82.70	$82.70
Purchase #3	$140.60	10.246%	$155.0059	$155.01	$155.00	$155.00
Purchase #4	$198.41	10.833%	$219.9038	$219.90	$219.90	$219.90
Purchase #5	$33.32	12.810%	$37.5883	$37.59	$37.60	$37.60
Purchase #6	$13.64	12.544%	$15.351	$15.35	$15.35	$15.40
Purchase #7	$101.61	9.860%	$111.6287	$111.63	$111.65	$111.60
7 purchase totals =	$577.92		$641.6936	$641.69	$641.70	$641.70