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	$78.67	6.590%	$83.8544	$83.85	$83.85	$83.90
Purchase #2	$62.65	5.503%	$66.0976	$66.10	$66.10	$66.10
Purchase #3	$25.70	12.870%	$29.0076	$29.01	$29.00	$29.00
Purchase #4	$122.67	4.204%	$127.827	$127.83	$127.85	$127.80
Purchase #5	$210.43	5.276%	$221.5323	$221.53	$221.55	$221.50
Purchase #6	$67.85	10.627%	$75.0604	$75.06	$75.05	$75.10
Purchase #7	$135.93	7.791%	$146.5203	$146.52	$146.50	$146.50
7 purchase totals =	$703.90		$749.8996	$749.90	$749.90	$749.90