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	$118.51	11.627%	$132.2892	$132.29	$132.30	$132.30
Purchase #2	$98.61	13.633%	$112.0535	$112.05	$112.05	$112.10
Purchase #3	$107.72	5.425%	$113.5638	$113.56	$113.55	$113.60
Purchase #4	$189.42	10.150%	$208.6461	$208.65	$208.65	$208.60
Purchase #5	$88.52	3.779%	$91.8652	$91.87	$91.85	$91.90
Purchase #6	$87.43	13.862%	$99.5495	$99.55	$99.55	$99.50
Purchase #7	$98.85	9.333%	$108.0757	$108.08	$108.10	$108.10
7 purchase totals =	$789.06		$866.0430	$866.05	$866.05	$866.10