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	$213.98	13.278%	$242.3923	$242.39	$242.40	$242.40
Purchase #2	$152.39	3.699%	$158.0269	$158.03	$158.05	$158.00
Purchase #3	$41.77	4.144%	$43.5009	$43.50	$43.50	$43.50
Purchase #4	$154.70	8.249%	$167.4612	$167.46	$167.45	$167.50
Purchase #5	$179.44	7.209%	$192.3758	$192.38	$192.40	$192.40
Purchase #6	$138.78	4.435%	$144.9349	$144.93	$144.95	$144.90
Purchase #7	$152.84	5.306%	$160.9497	$160.95	$160.95	$160.90
7 purchase totals =	$1,033.90		$1,109.6417	$1,109.64	$1,109.70	$1,109.60