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	$132.77	5.179%	$139.6462	$139.65	$139.65	$139.60
Purchase #2	$79.26	12.387%	$89.0779	$89.08	$89.10	$89.10
Purchase #3	$112.30	4.706%	$117.5848	$117.58	$117.60	$117.60
Purchase #4	$51.78	3.416%	$53.5488	$53.55	$53.55	$53.50
Purchase #5	$236.65	7.788%	$255.0803	$255.08	$255.10	$255.10
Purchase #6	$125.46	11.409%	$139.7737	$139.77	$139.75	$139.80
Purchase #7	$49.42	3.633%	$51.2154	$51.22	$51.20	$51.20
7 purchase totals =	$787.64		$845.9271	$845.93	$845.95	$845.90