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	$212.87	8.646%	$231.2747	$231.27	$231.25	$231.30
Purchase #2	$136.43	12.701%	$153.758	$153.76	$153.75	$153.80
Purchase #3	$150.45	5.282%	$158.3968	$158.40	$158.40	$158.40
Purchase #4	$63.66	12.208%	$71.4316	$71.43	$71.45	$71.40
Purchase #5	$172.55	6.538%	$183.8313	$183.83	$183.85	$183.80
Purchase #6	$127.77	9.585%	$140.0168	$140.02	$140.00	$140.00
Purchase #7	$132.55	7.656%	$142.698	$142.70	$142.70	$142.70
7 purchase totals =	$996.28		$1,081.4072	$1,081.41	$1,081.40	$1,081.40