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	$101.56	12.522%	$114.2773	$114.28	$114.30	$114.30
Purchase #2	$131.87	8.369%	$142.9062	$142.91	$142.90	$142.90
Purchase #3	$39.33	9.151%	$42.9291	$42.93	$42.95	$42.90
Purchase #4	$108.81	4.305%	$113.4943	$113.49	$113.50	$113.50
Purchase #5	$200.90	12.290%	$225.5906	$225.59	$225.60	$225.60
Purchase #6	$54.42	12.828%	$61.401	$61.40	$61.40	$61.40
Purchase #7	$33.50	10.738%	$37.0972	$37.10	$37.10	$37.10
7 purchase totals =	$670.39		$737.6957	$737.70	$737.75	$737.70