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	$36.26	12.828%	$40.9114	$40.91	$40.90	$40.90
Purchase #2	$149.34	5.854%	$158.0824	$158.08	$158.10	$158.10
Purchase #3	$32.43	3.405%	$33.5342	$33.53	$33.55	$33.50
Purchase #4	$51.83	9.718%	$56.8668	$56.87	$56.85	$56.90
Purchase #5	$104.82	3.594%	$108.5872	$108.59	$108.60	$108.60
Purchase #6	$142.46	12.651%	$160.4826	$160.48	$160.50	$160.50
Purchase #7	$145.85	7.343%	$156.5598	$156.56	$156.55	$156.60
7 purchase totals =	$662.99		$715.0244	$715.02	$715.05	$715.10