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	$58.70	7.186%	$62.9182	$62.92	$62.90	$62.90
Purchase #2	$168.91	6.438%	$179.7844	$179.78	$179.80	$179.80
Purchase #3	$66.47	10.492%	$73.444	$73.44	$73.45	$73.40
Purchase #4	$137.29	11.504%	$153.0838	$153.08	$153.10	$153.10
Purchase #5	$153.33	3.616%	$158.8744	$158.87	$158.85	$158.90
Purchase #6	$144.56	4.287%	$150.7573	$150.76	$150.75	$150.80
Purchase #7	$122.70	13.699%	$139.5087	$139.51	$139.50	$139.50
7 purchase totals =	$851.96		$918.3708	$918.36	$918.35	$918.40