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	$126.78	10.409%	$139.9765	$139.98	$140.00	$140.00
Purchase #2	$39.29	9.162%	$42.8897	$42.89	$42.90	$42.90
Purchase #3	$220.58	5.277%	$232.22	$232.22	$232.20	$232.20
Purchase #4	$52.97	12.506%	$59.5944	$59.59	$59.60	$59.60
Purchase #5	$33.26	9.857%	$36.5384	$36.54	$36.55	$36.50
Purchase #6	$65.54	12.455%	$73.703	$73.70	$73.70	$73.70
Purchase #7	$197.74	12.705%	$222.8629	$222.86	$222.85	$222.90
7 purchase totals =	$736.16		$807.7849	$807.78	$807.80	$807.80