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	$51.66	9.229%	$56.4277	$56.43	$56.45	$56.40
Purchase #2	$163.45	12.702%	$184.2114	$184.21	$184.20	$184.20
Purchase #3	$130.83	3.815%	$135.8212	$135.82	$135.80	$135.80
Purchase #4	$33.57	11.854%	$37.5494	$37.55	$37.55	$37.50
Purchase #5	$75.72	13.392%	$85.8604	$85.86	$85.85	$85.90
Purchase #6	$10.78	10.604%	$11.9231	$11.92	$11.90	$11.90
Purchase #7	$97.55	11.333%	$108.6053	$108.61	$108.60	$108.60
7 purchase totals =	$563.56		$620.3985	$620.40	$620.35	$620.30