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	$129.77	11.132%	$144.216	$144.22	$144.20	$144.20
Purchase #2	$215.83	4.605%	$225.769	$225.77	$225.75	$225.80
Purchase #3	$38.89	3.604%	$40.2916	$40.29	$40.30	$40.30
Purchase #4	$61.42	7.454%	$65.9982	$66.00	$66.00	$66.00
Purchase #5	$175.77	12.443%	$197.6411	$197.64	$197.65	$197.60
Purchase #6	$11.93	9.658%	$13.0822	$13.08	$13.10	$13.10
Purchase #7	$116.43	9.790%	$127.8285	$127.83	$127.85	$127.80
7 purchase totals =	$750.04		$814.8266	$814.83	$814.85	$814.80