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	$34.61	11.383%	$38.5497	$38.55	$38.55	$38.50
Purchase #2	$29.95	6.638%	$31.9381	$31.94	$31.95	$31.90
Purchase #3	$46.63	10.292%	$51.4292	$51.43	$51.45	$51.40
Purchase #4	$150.47	5.591%	$158.8828	$158.88	$158.90	$158.90
Purchase #5	$44.60	6.710%	$47.5927	$47.59	$47.60	$47.60
Purchase #6	$117.91	8.161%	$127.5326	$127.53	$127.55	$127.50
Purchase #7	$142.82	3.459%	$147.7601	$147.76	$147.75	$147.80
7 purchase totals =	$566.99		$603.6852	$603.68	$603.75	$603.60