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	$103.42	3.801%	$107.351	$107.35	$107.35	$107.40
Purchase #2	$161.59	9.110%	$176.3108	$176.31	$176.30	$176.30
Purchase #3	$117.43	6.106%	$124.6003	$124.60	$124.60	$124.60
Purchase #4	$134.97	6.719%	$144.0386	$144.04	$144.05	$144.00
Purchase #5	$204.40	9.535%	$223.8895	$223.89	$223.90	$223.90
Purchase #6	$248.54	12.629%	$279.9281	$279.93	$279.95	$279.90
Purchase #7	$59.88	13.457%	$67.9381	$67.94	$67.95	$67.90
7 purchase totals =	$1,030.23		$1,124.0564	$1,124.06	$1,124.10	$1,124.00