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	$42.66	6.640%	$45.4926	$45.49	$45.50	$45.50
Purchase #2	$222.65	8.427%	$241.4127	$241.41	$241.40	$241.40
Purchase #3	$177.50	9.554%	$194.4584	$194.46	$194.45	$194.50
Purchase #4	$12.86	6.126%	$13.6478	$13.65	$13.65	$13.60
Purchase #5	$153.62	12.772%	$173.2403	$173.24	$173.25	$173.20
Purchase #6	$80.50	8.811%	$87.5929	$87.59	$87.60	$87.60
Purchase #7	$74.94	11.538%	$83.5866	$83.59	$83.60	$83.60
7 purchase totals =	$764.73		$839.4313	$839.43	$839.45	$839.40