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	$40.55	5.695%	$42.8593	$42.86	$42.85	$42.90
Purchase #2	$155.85	9.358%	$170.4344	$170.43	$170.45	$170.40
Purchase #3	$124.38	9.815%	$136.5879	$136.59	$136.60	$136.60
Purchase #4	$141.50	3.576%	$146.56	$146.56	$146.55	$146.60
Purchase #5	$53.72	10.215%	$59.2075	$59.21	$59.20	$59.20
Purchase #6	$49.83	3.769%	$51.7081	$51.71	$51.70	$51.70
Purchase #7	$130.98	4.593%	$136.9959	$137.00	$137.00	$137.00
7 purchase totals =	$696.81		$744.3531	$744.36	$744.35	$744.40