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	$165.60	7.157%	$177.452	$177.45	$177.45	$177.50
Purchase #2	$230.47	4.243%	$240.2488	$240.25	$240.25	$240.20
Purchase #3	$94.95	8.650%	$103.1632	$103.16	$103.15	$103.20
Purchase #4	$36.35	6.239%	$38.6179	$38.62	$38.60	$38.60
Purchase #5	$45.86	13.654%	$52.1217	$52.12	$52.10	$52.10
Purchase #6	$81.58	10.749%	$90.349	$90.35	$90.35	$90.30
Purchase #7	$20.35	3.516%	$21.0655	$21.07	$21.05	$21.10
7 purchase totals =	$675.16		$723.0181	$723.02	$722.95	$723.00